All categories

3 years ago

Help ! solve the following system of equations -9x+2y=-13 2x-9y=20

Mathematics

1 answer:

Stella [2.4K]3 years ago

5 0

Answer: x = 1, y = -2

Step-by-step explanation:

-9x+2y=-13

x= 13/9 + 2/9y

2x-9y=20

2(13/9+2/9y)-9y=20

Substitute y with -2.

x= 13/9+2/9(-2)

After solving you'll see that 1 is a possible solution for x.

Check your answer

-9x+2y=-13

-9x1+2(-2) = -13

2x-9y=20

2x1-9(-2) = 20

-13 = -13

20 = 20

Therefore, x=1 and y=-2

You might be interested in

A norman window is constructed by adjoining a semicircle to the top of an ordinary rectangular. Find the dimensions of a norman

Yanka [14]

Answer:

$W\approx 8.72$ and $L\approx 15.57$ .

Step-by-step explanation:

Please find the attachment.

We have been given that a norman window is constructed by adjoining a semicircle to the top of an ordinary rectangular. The total perimeter is 38 feet.

The perimeter of the window will be equal to three sides of rectangle plus half the perimeter of circle. We can represent our given information in an equation as:

$2L+W+\frac{1}{2}(2\pi r)=38$

We can see that diameter of semicircle is W. We know that diameter is twice the radius, so we will get:

$2L+W+\frac{1}{2}(2r\pi)=38$

$2L+W+\frac{\pi}{2}W=38$

Let us find area of window equation as:

$\text{Area}=W\cdot L+\frac{1}{2}(\pi r^2)$

$\text{Area}=W\cdot L+\frac{1}{2}(\pi (\frac{W}{2})^2)$

$\text{Area}=W\cdot L+\frac{\pi}{2}(\frac{W}{2})^2)$

$\text{Area}=W\cdot L+\frac{\pi}{2}(\frac{W^2}{4})$

$\text{Area}=W\cdot L+\frac{\pi}{8}W^2$

Now, we will solve for L is terms W from perimeter equation as:

$L=38-(W+\frac{\pi }{2}W)$

Substitute this value in area equation:

$A=W\cdot (38-W-\frac{\pi }{2}W)+\frac{\pi}{8}W^2$

Since we need the area of window to maximize, so we need to optimize area equation.

$A=W\cdot (38-W-\frac{\pi }{2}W)+\frac{\pi}{8}W^2$

$A=38W-W^2-\frac{\pi }{2}W^2+\frac{\pi}{8}W^2$

Let us find derivative of area equation as:

$A'=38-2W-\frac{2\pi }{2}W+\frac{2\pi}{8}W$

$A'=38-2W-\pi W+\frac{\pi}{4}W$

$A'=38-2W-\frac{4\pi W}{4}+\frac{\pi}{4}W$

$A'=38-2W-\frac{3\pi W}{4}$

To find maxima, we will equate first derivative equal to 0 as:

$38-2W-\frac{3\pi W}{4}=0$

$-2W-\frac{3\pi W}{4}=-38$

$\frac{-8W-3\pi W}{4}=-38$

$\frac{-8W-3\pi W}{4}*4=-38*4$

$-8W-3\pi W=-152$

$8W+3\pi W=152$

$W(8+3\pi)=152$

$W=\frac{152}{8+3\pi}$

$W=8.723210$

$W\approx 8.72$

Upon substituting $W=8.723210$ in equation $L=38-(W+\frac{\pi }{2}W)$ , we will get:

$L=38-(8.723210+\frac{\pi }{2}8.723210)$

$L=38-(8.723210+\frac{8.723210\pi }{2})$

$L=38-(8.723210+\frac{27.40477245}{2})$

$L=38-(8.723210+13.70238622)$

$L=38-(22.42559622)$

$L=15.57440378$

$L\approx 15.57$

Therefore, the dimensions of the window that will maximize the area would be $W\approx 8.72$ and $L\approx 15.57$ .

8 0

3 years ago

A number increased by 7

postnew [5]

Answer:

x+7

Step-by-step explanation:

7 0

3 years ago

2 3 2/15+ 5 2 8/15+ 1 6 1/15=

allsm [11]

Answer:

91 11/15

Step-by-step explanation:

23+2/15+52+8/15+16+1/15

=23+52+16+2/15+8/15+1/15

=91+11/15

8 0

3 years ago

Read 2 more answers

A recent study was conducted to explore the relationship between the weight of a car and miles per gallon (gas mileage). A linea

k0ka [10]

Answer: a. iv. The weight of a car can be used to explain about 79.6% of the variability in gas mileage using a linear relationship.

b. ii. There is a fairly strong, negative relationship between car weight and miles per gallon.

Step-by-step explanation:

A coefficient of determination (denoted by R²) is a measure in a regression model that determines proportion of the variance in the dependent quantity that is predictable from the independent quantity.

It is square of correlation coefficient (R).

Here, independent quantity = weight of a car

dependent quantity = miles per gallon (gas mileage)

The coefficient of determination (R²) was reported to be 79.6%.

That means, The weight of a car can be used to explain about 79.6% of the variability in gas mileage using a linear relationship.

A correlation coefficient(R) tells about the strength and direction of relation .
It lies between -1 and 1.

For the study, the correlation coefficient R is -0.8921.

There is a fairly strong, negative relationship between car weight and miles per gallon.

7 0

3 years ago

24 inches is equal to how many feet

cupoosta [38]

The answer is 2 feet it is equal to two feet

3 0

3 years ago

Read 2 more answers