Answers
Step 1: Find the area of the rectangle
A = base x height
A = 39 x 20
A = 780
Step 2: Find the area of the semi-circles
---Two semi-circles is the same as one whole circle, so I will be finding the area of one whole circle.
A = pi x r^2
A = pi x 10^2
A = 100pi = 314
Step 3: Find the area of the figure
Area = area of the rectangle - area of the semi-circles
A = 780 - 314
A = 466 cm^2
Hope this helps!
Answer:
466 cm^2
Step-by-step explanation:
This one is done basically the same as the other.
Rectangle = 20 x 39
Circle = (3.14) x 10^2
Rectangle = 780
Circle = 314
rectangle - circle
780 - 314 = 466
Related Questions
A company is planning its spring advertising campaign. Its marketing team is planning to mail out different types of advertisements, at random, to their town's residents each week. They have the following types of advertisements ready:
Week 1 Week 2 Week 3
Small Poster Brochure Business Card
Brochur Leaflet Postcard
Postcard Small Poster
How many different possible ways can a resident receive an advertisement?
Answers
Answer:
The answer is "18".
Step-by-step explanation:
Amount of different methods a resident could get an advertisement:
[tex]=2\times 3 \times 3\\\\= 18[/tex]
Answer:
The Answer is 18
Step-by-step explanation:
2*3*3
Five subtracted from seven times a number is 9. What is the number?
A) Translate the statement above into an equation that you can solve to answer this question. Do not solve it yet. Use
x
as your variable.
The equation is _____________
B) Solve your equation in part [A] for
Answer:
x=
Answers
Answer:
18
Step-by-step explanation:
7-5=2
2x9=18
14-5=9
9=7n-5
9=7n-5
9=7(2)-5
9=14-5
9=9
I could be wrong an misunderstood the entire thing, however I can reassure you 18 is not the answer as the question states “Five subtracted from seven times a number is 9”, therefore the final answer in part A) needs to equal 9.
someone help me pls i need to pass summer school
Answers
Answer:
A
Step-by-step explanation:
The be the inverse function the domain {4,5,6,7} becomes the range and the range {14,12,10,8} becomes the domain
14 → 4
12 →5
10 →6
8 →7
Mua hàng hóa 10000kg về nhập kho,Đơn giá 200 000đ/kg,thuế gtgt là 10%,trả bằng chuyển khoản 50%,còn nợ người bán.Chi phí vận chuyển 2 100 000 bao gồm thueest gtgt 5% trả tiền mặt
Answers
Write an equation for the following: y varies directly with x. Find K
when x=4 and y=5.
Answers
Answer:
4/5
Step-by-step explanation:
y varies as x
y=kx
k=x/y
Please help no links.Mr. Longley is buying a $15 box of trail mix at Whole Foods, where tax is 6%. If Mr. Longley has
a coupon for 10% off the price of any item, how much does he end up paying?
I
Answers
Answer:
$14.40
Step-by-step explanation:
my way of doing things:
15/100=0.15=1%of total amount
0.15 x 6=0.9= the 6% which is the tax
0.15 x 10 = 1.5=the coupon
Take the coupon amount $1.50 minus the tax amount $0.90 =$0.60. Because the coupon amount is greater than the tax the 60 cents gets taken away from the original 15 dollars leaving Mr. Longely only having to pay $14.40.
Which best describes the relationship between the line that passes through the points (6, -1) and (11, 2) and the line that passes through the
points (5-7) and (8-2)?
Answers
Answer:
D. Neither perpendicular nor parallel
Step-by-step explanation:
Let's find the slope (m) of both lines:
✔️Slope (m) of the line that passes through (6, -1) and (11, 2):
Slope (m) = change in y/change in x
Slope (m) = (2 -(-1))/(11 - 6) = 3/5
✔️Slope (m) of the line that passes through (5, -7) and (8, -2)
Slope (m) = change in y/change in x
Slope (m) = (-2 -(-7))/(8 - 5) = 5/3
✅The slope of both lines are not the same, therefore they are not parallel nor same line.
Also, the slope of one is not the negative reciprocal of the other, therefore they are not perpendicular.
n rectangle ABCD, point E lies half way between sides AB and CD and halfway between sides AD and BC. If AB=3 and BC=11, what is the area of the shaded region? Write your answer as a decimal, if necessary. Do not include units in your answer.
Answers
*see attachment for clearer diagram
Answer:
16.5
Step-by-step explanation:
BC = 11
AB = 3
Area of the shaded region = area of ∆AEB + area of ∆CED
Area of a triangle is given as,
A = ½*base*height
Find the area of each triangle and add together
✔️Area of ∆AEB = ½*bh
Where,
base (b) = 3
height (h) = ½(BC) = ½(11) = 5.5
Area of ∆AEB = ½*3*5.5 = 8.25
✔️Area of ∆CED = ½*bh
Where,
b = 3
h = ½(BC) = ½(11) = 5.5
Area of ∆CED = ½*3*5.5 = 8.25
✅Area of the shaded region = area of ∆AEB + area of ∆CED
= 8.25 + 8.25
= 16.5
Triangle ABL is an isosceles triangle in circle A with a radius of 11, PL = 16, and ∠PAL = 93°. Find the area of the circle enclosed by line PL and arc PL. Show all work and round your answer to two decimal places.
Answers
The area bounded by a chord and arc it intercepts is known as a segment of a circle segment of a circle
The area of the circle enclosed by line PL and arc PL is approximately 37.62 square units
The reason the above value is correct is as follows:
The given parameters in the question are;
The radius of the circle, r = 11
The length of the chord PL = 16
The measure of angle ∠PAL = 93°
Required:
The area of part of the circle enclosed by chord PL and arc PL
Solution:
The shaded area of the given circle is the minor segment of the circle enclosed by line PL and arc PL
The area of a segment of a circle is given by the following formula;
Area of segment = Area of the sector - Area of the triangle
Area of segment = Area of minor sector APL - Area of triangle APL
Area of minor sector APL:
Area of a sector = (θ/360)×π·r²
Where;
r = The radius of the circle
θ = The angle of the sector of the circle
Plugging in the the values of r and θ, we get;
Area of the minor sector APL = (93°/360°) × π × 11² ≈ 98.2 square units
Area of Triangle APL:
Area of a triangle = (1/2) × Base length × Height
Therefore;
The area of ΔAPL = (1/2) × 16 × 11 × cos(93°/2) ≈ 60.58 square units
Required shaded area enclosed by line PL and arc PL:
Therefore, the area of shaded segment enclosed by line PL and arc PL is found as follows;
Area of the required segment PL ≈ (98.2 - 60.58) square units = 37.62 square units
The area of the circle enclosed by line PL and arc PL ≈ 37.62 square units
Learn more about the finding the area of a segment can be found here:
https://brainly.com/question/22599425
The area of the circle enclosed by line segment PL and circle arc PL is 37.80 square units.
The calculation of the area between line segment PL and circle arc PL is described below:
1) Calculation of the area of the circle arc.
2) Calculation of the area of the triangle.
3) Subtracting the area found in 2) from the area found in 1).
Step 1:
The area of a circle arc is determined by the following formula:
[tex]A_{ca} = \frac{\alpha\cdot \pi\cdot r^{2}}{360}[/tex] (1)
Where:
[tex]A_{ca}[/tex] - Area of the circle arc.
[tex]\alpha[/tex] - Arc angle, in sexagesimal degrees.
[tex]r[/tex] - Radius.
If we know that [tex]\alpha = 93^{\circ}[/tex] and [tex]r = 11[/tex], then the area of the circle arc is:
[tex]A_{ca} = \frac{93\cdot \pi\cdot 11^{2}}{360}[/tex]
[tex]A_{ca} \approx 98.201[/tex]
Step 2:
The area of the triangle is determined by Heron's formula:
[tex]A_{t} = \sqrt{s\cdot (s-l)\cdot (s-r)^{2}}[/tex] (2)
[tex]s = \frac{l + 2\cdot r}{2}[/tex]
Where:
[tex]A_{t}[/tex] - Area of the triangle.
[tex]r[/tex] - Radius.
[tex]l[/tex] - Length of the line segment PL.
If we know that [tex]l = 16[/tex] and [tex]r = 11[/tex], then the area of the triangle is:
[tex]s = \frac{16+2\cdot (11)}{2}[/tex]
[tex]s = 19[/tex]
[tex]A_{t} = \sqrt{19\cdot (19-16)\cdot (19-11)^{2}}[/tex]
[tex]A_{t} \approx 60.399[/tex]
Step 3:
And the area between the line segment PL and the circle arc PL is:
[tex]A_{s} = A_{ca}-A_{t}[/tex]
[tex]A_{s} = 98.201 - 60.399[/tex]
[tex]A_{s} = 37.802[/tex]
The area of the circle enclosed by line segment PL and circle arc PL is 37.80 square units.
The length of a rectangle is 4 meters longer than the width. If the area is 22 square meters. find the rectangles dimensions. The width is what? The length is what?
Answers
Answer:
The width is:
[tex]-2+\sqrt{26}\text{ meters}\text{ }(\text{or approximately 3.0990 meters})[/tex]
And the length is:
[tex]2+\sqrt{26}\text{ meters}\text{ } (\text{or approximately 7.0990 meters})[/tex]
Step-by-step explanation:
Recall that the area of a rectangle is given by:
[tex]\displaystyle A = w\ell[/tex]
Where w is the width and l is the length.
We are given that the length of a rectangle is four meters longer than the width. Thus:
[tex]\ell = w + 4[/tex]
And we also know that the area of the rectangle is 22 square meteres.
Substitute:
[tex](22)=w(w+4)[/tex]
Distribute and isolate the equation:
[tex]w^2+4w-22=0[/tex]
The equation isn't factorable, so we can instead use the quadratic formula:
[tex]\displaystyle w = \frac{-b\pm\sqrt{b^2-4ac}}{2a}[/tex]
In this case, a = 1, b = 4, and c = -22. Substitute:
[tex]\displaystyle w = \frac{-(4)\pm\sqrt{(4)^2-4(1)(-22)}}{2(1)}[/tex]
Evaluate:
[tex]\displaystyle\begin{aligned} w &= \frac{-4\pm\sqrt{104}}{2}\\ \\ &=\frac{-4\pm\sqrt{4\cdot 26}}{2} \\ \\ &=\frac{-4\pm2\sqrt{26}}{2} \\ \\ & = -2\pm \sqrt{26} \end{aligned}[/tex]
Thus, our two solutions are:
[tex]w_1=-2+\sqrt{26}\approx 3.0990\text{ or } w_2=-2-\sqrt{26}\approx-7.0990[/tex]
Since the width cannot be negative, we can ignore the second solution.
Since the length is four meters longer than the width:
[tex]\ell = (-2+\sqrt{26})+4=2+\sqrt{26}\text{ meters}[/tex]
Thus, the dimensions of the rectangle are:
[tex]\displaystyle (2+\sqrt{26}) \text{ meters by } (-2+\sqrt{26})\text{ meters}[/tex]
Or, approximately 3.0990 by 7.0990.
Please help 20 points. I will give Brainly to who ever get it right.
Answers
Answer:
Step-by-step explanation:
(-∞,2)
The sum of two numbers is -17. Their difference is 41. Find the numbers
Answers
Answer:
x = 12
y = -29
Step-by-step explanation:
Our given equations: x + y = -17 and x - y = 41
Solve for x and substitute.
x = -17 - y
(-17 - y) - y = 41
-17 - 2y = 41
2y = -58
y = -29
Solve for x using y
x + (-29) = -17
x = 12
If the function y=x^5 is transformed to y=x^5+3 what’s the statement
Answers
I dont know what you mean by the question but according to me.
If y=x^5
y=x^5+3
Then y+3=x^5+3
Answered by Gauthmath must click thanks and mark brainliest
An internet provider states that, on average, the daily amount of time an adult spends on the internet is 4.5 hours. A sociologist studying the behaviors of internet consumers believes the average daily amount an adult spends on the internet is different than the amount stated by the internet provider. After completing a study, the sociologist found that the average daily amount of time an adult spends on the internet is 5.9 hours, on average. As the sociologist sets up a hypothesis test to determine if their belief is correct, what is their claim?
a. The average daily amount of time an adult spends on the internet is different than 4.5 hours.
b. The average daily amount of time an adult spends on the internet is different than 5.9 hours.
c. Adults spend a majority of their time on the internet.
d. The average daily amount of time an adult spends on the internet is 4.5 hours.
Answers
Answer:
a. The average daily amount of time an adult spends on the internet is different than 4.5 hours.
Step-by-step explanation:
An internet provider states that, on average, the daily amount of time an adult spends on the internet is 4.5 hours.
At the null hypothesis, it is claimed that the mean is of 4.5 hours, that is:
[tex]H_0: \mu = 4.5[/tex]
A sociologist studying the behaviors of internet consumers believes the average daily amount an adult spends on the internet is different than the amount stated by the internet provider.
At the alternative hypothesis, the sociologist claim, is that the mean is different of 4.5, that is:
[tex]H_1: \mu \neq 4.5[/tex]
Thus, the correct answer is given by option a.
What type of line is PQ?
A. side bisector
B. angle bisector
C. median
D. altitude
Answers
Answer:
B: I think
Step-by-step explanation:
correct me if im wrong
The line PQ is an angle bisector because it divides the angle P into two equal half option (B) angle bisector is correct.
What is an angle?When two lines or rays converge at the same point, the measurement between them is called a "Angle."
We have a triangle shown in the picture.
As we know,
in terms of geometry, the triangle is a three-sided polygon with three edges and three vertices. The triangle's interior angles add up to 180°.
From the figure the segment PQ divides the angle into two equal half.
From the definition of the angle bisector, the angle bisector can be defined as a line segment that divides the angle into two half.
Angle P = 40 + 40 = 80 degrees
Thus, the line PQ is an angle bisector because it divides the angle P into two equal half option (B) angle bisector is correct.
Learn more about the angle here:
brainly.com/question/7116550
#SPJ5
The vertex form of the equation of a parabola is y =
standard form of the equation?
Y=1/2(x - 4)^2 +13. What is the
O A. y-2x2-8x+29
O B. y=zx2 - 4x +21
O C. y=1* -8x+21
O D. y - 4x2 - 4x +29
Answers
Answer:
Step-by-step explanation:
y = ½(x-4)² + 13
y = ½(x² - 8x + 16) + 13
y = ½x² - 4x + 21
Three Nissans, two Fords, and four Chevrolets can be rented for $106 per day. At the same rates two Nissans, four Fords, and three Chevrolets cost $107 per day, whereas four Nissans, three Fords, and two Chevrolets cost $102 per day. Find the rental rate for the Fords.
Answers
Answer:
The rental rate for the Fords is of $12 per day.
Step-by-step explanation:
This question is solved using a system of equations.
I am going to say that:
x is the cost of a Nissan.
y is the cost of a Ford.
z is the cost of a Chevrolet.
Three Nissans, two Fords, and four Chevrolets can be rented for $106 per day.
This means that:
[tex]3x + 2y + 4z = 106[/tex]
Two Nissans, four Fords, and three Chevrolets cost $107 per day
This means that:
[tex]2x + 4y + 3z = 107[/tex]
Four Nissans, three Fords, and two Chevrolets cost $102 per day.
This means that:
[tex]4x + 3y + 2z = 102[/tex]
From the first equation:
[tex]4z = 106 - 3x - 2y[/tex]
[tex]2z = 53 - 1.5x - y[/tex]
[tex]z = 26.5 - 0.75x - 0.5y[/tex]
Replacing into the third equation:
[tex]4x + 3y + 53 - 1.5x - y = 102[/tex]
[tex]2.5x + 2y = 49[/tex]
From the second equation:
[tex]2x + 4y + 3z = 107[/tex]
[tex]2x = 107 - 4y - 3z[/tex]
[tex]x = 53.5 - 2y - 1.5z[/tex]
[tex]x = 53.5 - 2y - 1.5(26.5 - 0.75x - 0.5y)[/tex]
[tex]x - 1.125x = 53.5 - 2y - 39.75 + 0.75y[/tex]
[tex]-0.125x = 13.75 - 1.25y[/tex]
[tex]0.125x = 1.25y - 13.75[/tex]
[tex]x = \frac{1.25y - 13.75}{0.125}[/tex]
[tex]x = 10y - 110[/tex]
Find the rental rate for the Fords.
We have to find y, so:
[tex]2.5x + 2y = 49[/tex]
[tex]2.5(10y - 110) + 2y = 49[/tex]
[tex]25y - 275 + 2y = 49[/tex]
[tex]27y = 324[/tex]
[tex]y = \frac{324}{27}[/tex]
[tex]y = 12[/tex]
The rental rate for the Fords is of $12 per day.
The first term of an A.P is -8.the ratio of the 7th term to the 9th term is 5:8.calculate the numbers
Answers
Answer:
The 7th term is 10 and the 9th term is 16
(and the common difference d = 3)
Step-by-step explanation:
If by calculate the numbers, you mean the 7th term and 9th term, first, you will determine the common difference.
The nth term of an A.P is given by the formula
Tₙ= a+(n-1)d
Where Tₙ is the nth term
a is the first term
and d is the common difference
From the question,
a = -8
T₇ : T₉ = 5:8
From the formula
T₇ = a + (7-1)d = a + 6d
and T₉ = a + (9-1)d = a + 8d
Then.
a + 6d : a + 8d = 5:8
But a = -8
∴ -8 + 6d : -8 + 8d = 5:8
We can write that
(-8 + 6d) / (-8 + 8d) = 5/8
Cross multiply
8(-8+6d) = 5(-8+8d)
-64 + 48d = -40 + 40d
48d - 40d = -40 + 64
8d = 24
d = 24/8
d = 3
∴ The common difference is 3
Now, for the 7th term
From
T₇ = a + 6d
T₇ = -8 + 6(3)
T₇ = -8 + 18
T₇ = 10
and for the 9th term
T₉ = a + 8d
T₉ = -8 + 8(3)
T₉ = -8 + 24
T₉ = 16
Hence, the 7th term is 10 and the 9th term is 16
Evaluate the following
sqrt(25x169)
Answers
Step-by-step explanation:
[tex]what \: is \: the \: value \: of \: 5 \times 13 = 65 \: is \: the \: answer[/tex]
Answer:
65
Step-by-step explanation:
[tex] \sqrt{25 \times 169} [/tex]
[tex] \sqrt{5 \times 5 \times 13 \times 13} [/tex]
[tex]5 \times 13[/tex]
[tex]65[/tex]
I hope this helps you
1/10
9/10
Q
Find the perimeter of the rectangle pictured above. Give your answer as a reduced mixed number.
Answers
Answer:2
Step-by-step explanation:
URGENT 100 POINTS AND BRAINIEST!!!!!!
Question 4 (Essay Worth 10 points)
(02.05 HC)
The linear functions f(x) and g(x) are represented on the graph, where g(x) is a transformation of f(x):
A graph with two linear functions; f of x passes through 5, 0 and 10, 10, and g of x passes through negative 3, 0 and 2, 10.
Part A: Describe two types of transformations that can be used to transform f(x) to g(x). (2 points)
Part B: Solve for k in each type of transformation. (4 points)
Part C: Write an equation for each type of transformation that can be used to transform f(x) to g(x). (4 points)
Answers
Using the points stated in the original problem, I have determined the lines for the graph.
f(x)=3x-1
g(x)= 3x+17
Using the basic descriptions of transformations, we can determine the movement of the lines as being either horizontal or vertical shifts. (to put a visual to this problem, I the diagram in Desmos and then marked the stated points on the graph.)
Horizontal shifts move the line either to the left or to the right. Vertical shifts move the line either up or down.
If you look at the graphs as being the same x-value for the functions, the change in the y- value is +18, which is a vertical shift.
If you look at the graphs as being the same y-values, the change in x is -6 which is a horizontal shift.
So, the value of k is the amount of change each equation has to have to match the points given. (from f(x) to g(x))
The vertical shift is g(x)=f(x) +18
The horizontal shift is g(x)=f(x-6)
Answer:
The vertical shift is g(x)=f(x) +18
The horizontal shift is g(x)=f(x-6)
Step-by-step explanation:
A farmer's silo is the shape of a cylinder with a hemisphere as the roof. If the height of the silo is 101 feet and the radius of the hemisphere is r feet. Express the volume of the silo as a function of r.
Answers
Answer:
[tex]V(r) =101\pi r^2 + \frac{2}{3}\pi r^3[/tex]
Step-by-step explanation:
Given
Shapes: cylinder and hemisphere
[tex]h = 101[/tex] --- height of cylinder
Required
The volume of the silo
The volume is calculated as:
Volume (V) = Volume of cylinder (V1) + Volume of hemisphere (V2)
So, we have:
[tex]V_1 = \pi r^2h[/tex]
[tex]V_1 = \pi r^2 * 101[/tex]
[tex]V_1 = 101\pi r^2[/tex] --- cylinder
[tex]V_2 = \frac{2}{3}\pi r^3[/tex] ---- hemisphere
So, the volume of the silo is:
[tex]V =V_1 + V_2[/tex]
[tex]V =101\pi r^2 + \frac{2}{3}\pi r^3[/tex]
Write as a function
[tex]V(r) =101\pi r^2 + \frac{2}{3}\pi r^3[/tex]
Where: [tex]\pi = \frac{22}{7}[/tex]
Plz help me find x and y on these triangles
Answers
Answer:
x=15, y=2
Step-by-step explanation:
By AA similarity, the triangles are similar. Therefore, we can find the ratios of the side lengths.
9/3=3=ratio of the side length of a larger triangle to a smaller one.
3=6/y, y=2
3=x/5, x=15
Hope this helped,
~cloud
List the sides of the triangle in order from largest to smallest.
Answers
Write the equation of the line in fully simplified slope-intercept form.
Answers
Answer:
y = -1x + 2
Step-by-step explanation:
50 times what equals 10 million
Answers
Explanation: divide 10,000,000 by 50 and it gives you the answer
200,000
Step-by-step explanation:
50 times what equals 10 million?
Write the expression in algebraic form.
50x = 10,000,000
Divide 10,000,000 by 50.
x = 200,000
Therefore, 50 times 200,000 equals 10 million
Find the missing side round your answer to the nearest tenth.
Answers
Answer: 20.5
Step-by-step explanation:
Cos 43 = X/28
O.73 = x/28
(0.73)(28)=20.5
A certain drug is used to treat asthma. In a clinical trial of theâ drug, 17 of 258 treated subjects experienced headachesâ (based on data from theâ manufacturer). The accompanying calculator display shows results from a test of the claim that less than 11â% of treated subjects experienced headaches. Use the normal distribution as an approximation to the binomial distribution and assume a 0.01 significance level to complete partsâ (a) throughâ (e) below. â
1-PropZTest
prop<0.11
z=â2.264337000
p=0.0117766978
p=0.0658914729
n=258
a. Is the testâ two-tailed, left-tailed, orâ right-tailed?
b. What is the best statistics?
c. What is the P-value?
d. What is the nut hypothesis and what do you conclude who det hypothesis?
Identify the null hypothesis.
A. H0: pâ 0.11.
B. H0: p=0.11.
C. H0: p<0.11.
D. H0: p>0.11.
Decide whether to reject the null hypothesis.
A. Reject the null hypothesis because theâ P-value is greater than α.
B. Fail to reject the null hypothesis because theâ P-value is less than or equal to α.
C. Reject the null hypothesis because theâ P-value is less than or equal to α.
D. Fail to reject the null hypothesis because theâ P-value is greater than α
e. What is the finalâ conclusion?
A. There is not sufficient evidence to warrant rejection of the claim that less than 11â% of treated subjects experienced headaches.
B. There is not sufficient evidence to support the claim that less than 11â% of treated subjects experienced headaches.
C. There is sufficient evidence to support the claim that less than 11â% of treated subjects experienced headaches.
D. There is sufficient evidence to warrant rejection of the claim that less than 11â% of treated subjects experienced headaches.
Answers
Solution :
a). The test is a left tailed test.
b). The sample proportion is :
[tex]$\hat p = \frac{x}{n}$[/tex]
[tex]$\hat p = \frac{17}{258}$[/tex]
= 0.065
Determining the Z statistics using the formula :
[tex]$Z=\frac{\hat p - p}{\sqrt{\frac{p(1-p)}{n}}}$[/tex]
[tex]$Z=\frac{0.065 - 0.11}{\sqrt{\frac{0.11(1-0.11)}{258}}}$[/tex]
= -2.31
∴ Z statistics value is -2.31
c). Using the excel function, the P-value is :
P-value = Normsdist(-2.31)
= 0.0104441
d). The null hypothesis is [tex]$H_0: P = 0.11$[/tex]
The level of significance is 0.01
We fail to reject the null hypothesis as the P value is less than or equal to the significant level.
Which equation can she use as statement 5? 60:x = 48:(48 + 36) 60 + x = 48 + 36 60 − x = 48 − 36 60:(60 + x) = 48:(48 + 36)
Answers
NO LINKS OR ANSWERING QUESTIONS YOU DON'T KNOW!! Part 2.
2. What is a determinant and what role does it play with matrices (Hint: What does a determinant of 0 mean)? How can this be used when solving systems of equations?
Answers
9514 1404 393
Explanation:
Definition
The determinant of a square matrix is a single number that is computed (recursively) as the sum of products of the elements of a row or column and the determinants of their cofactors. The determinant of a single element is the value of that element.
The cofactor of an element in an n by n matrix is the (n-1) by (n-1) matrix that results when the row and column of that element are deleted. The "appropriate sign" of the element is applied to the cofactor matrix. The "appropriate sign" of an element is positive if the sum of its row and column numbers is even, negative otherwise. (Rows and columns are considered to be numbered 1 to n in an n by n matrix.)
Uses
The inverse of a square matrix is the transpose of the cofactor matrix, divided by the determinant. Hence if the determinant is zero, the inverse matrix is undefined. This means any system of equations the matrix might represent will have no distinct solution. (There may be zero solutions, or there may be an infinite number of solutions. The determinant by itself cannot tell you which.)
Cramer's Rule for the solution of linear systems of equations specifies that the value of any given variable is the ratio of the determinants of two matrices. The numerator matrix is the original matrix with the coefficients of the variable replaced by the constants in the standard-form equations; the denominator matrix is the original coefficient matrix. This rule lets you solve a system of 3 equations in 3 variables by computing 3+1 = 4 determinants, for example.
Let's look at an example.
If we wanted to solve this system of equations
[tex]\begin{cases}2x-y = 2\\x+y = 7\end{cases}[/tex]
Then it's equivalent to solving this matrix equation
[tex]\begin{bmatrix}2 & -1\\1 & 1\end{bmatrix}\begin{bmatrix}x\\y\end{bmatrix}=\begin{bmatrix}2\\7\end{bmatrix}[/tex]
We can then further condense that into the form
[tex]Aw = B[/tex]
Where,
[tex]A = \begin{bmatrix}2 & -1\\1 & 1\end{bmatrix}\\\\w = \begin{bmatrix}x\\y\end{bmatrix}\\\\B = \begin{bmatrix}2\\7\end{bmatrix}[/tex]
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To solve the matrix equation Aw = B, we could compute the inverse matrix [tex]A^{-1}[/tex] and left-multiply both sides by this to isolate w.
So we'd go from [tex]Aw=B[/tex] to [tex]w = A^{-1}*B[/tex]. The order of multiplication is important.
For any 2x2 matrix of the form
[tex]P = \begin{bmatrix}a & b\\c & d\end{bmatrix}[/tex]
its inverse is
[tex]P^{-1} = \frac{1}{ad-bc}\begin{bmatrix}d & -b\\-c & a\end{bmatrix}[/tex]
Notice the expression ad-bc in the denominator of that fractional term outside. This [tex]ad-bc[/tex] expression represents the determinant of matrix P. Some books may use the notation "det" to mean "determinant"
[tex]P^{-1} = \frac{1}{\det(P)}\begin{bmatrix}d & -b\\-c & a\end{bmatrix}[/tex]
or you may see it written as
[tex]P^{-1} = \frac{1}{|P|}\begin{bmatrix}d & -b\\-c & a\end{bmatrix}[/tex]
Those aren't absolute value bars, even if they may look like it.
Based on that, we can see that the determinant must be nonzero in order to compute the inverse of the matrix. Consequently, the determinant must be nonzero in order for Aw = B to have one solution.
If the determinant is 0, then we have two possibilities:
There are infinitely many solutions (aka the system is dependent)There are no solutions (the system is inconsistent)So a zero determinant would have to be investigated further as to which outcome would occur.
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Let's return to the example and compute the inverse (if possible).
[tex]A = \begin{bmatrix}2 & -1\\1 & 1\end{bmatrix}\\\\A^{-1} = \frac{1}{2*1 - (-1)*1}\begin{bmatrix}1 & 1\\-1 & 2\end{bmatrix}\\\\A^{-1} = \frac{1}{3}\begin{bmatrix}1 & 1\\-1 & 2\end{bmatrix}\\\\[/tex]
In this case, the inverse does exist.
This further leads to
[tex]w = A^{-1}*B\\\\w = \frac{1}{3}\begin{bmatrix}1 & 1\\-1 & 2\end{bmatrix}*\begin{bmatrix}2\\7\end{bmatrix}\\\\w = \frac{1}{3}\begin{bmatrix}1*2+1*7\\-1*2+2*7\end{bmatrix}\\\\w = \frac{1}{3}\begin{bmatrix}9\\12\end{bmatrix}\\\\w = \begin{bmatrix}(1/3)*9\\(1/3)*12\end{bmatrix}\\\\w = \begin{bmatrix}3\\4\end{bmatrix}\\\\\begin{bmatrix}x\\y\end{bmatrix} = \begin{bmatrix}3\\4\end{bmatrix}\\\\[/tex]
This shows that the solution is (x,y) = (3,4).
As the other person pointed out, you could use Cramer's Rule to solve this system. Cramer's Rule will involve using determinants and you'll be dividing over determinants. So this is another reason why we cannot have a zero determinant.
