Question

If x+y=15 and x-y=25, then what is the value of 2x^2 - y^2?

Answer 1

775

Explanation:

We are given two equations in which we can perform systems of equations by putting these two equations on top of each other then solving for one variable:

x+y=15

x-y=25

Here, we can cancel out the y variable and get:

2x=40

x=20

Then we can put the x variable into any of the equations to solve for y (in this case I will use the equation x+y=15 so 20+y=15

y=-5

Now, we can solve by plugging both variables into 2x^2 - y^2 :

2(20)^2 - (-5)^2

800-25 = 775

I hope this helps!

Answer 2

775

Explanation:

Hi there!

We are given the following system of equations:

x+y=15

x-y=25

and we need to find the value of 2x²-y²

First, let's find the value of x and y

Let's add the 2 equations together to clear y and solve for x (y-y=0)

2x=40

divide both sides by 2

x=20

Now substitute 20 as x into either one of the equations to solve for y

To do x-y=25 for instance,

20-y=25

subtract 20 from both sides

-y=5

multiply both sides by -1

y=-5

Now we know that x=20 and y=-5

Substitute those values into the expression (remember: y² is equal to y×y, or (y)²)

2(20)²-(-5)²

Raise to the second power

2(400)-(25)

multiply and open parenthesis

800-25

subtract

775

Hope this helps!