Question

3x +y = -2x+8

-3x+2y=-10
If (x,y) is a solution to the system of equations
above, what is the value of xy?

a) -16
b) -8
c) -4
d) 4

Answer 1

Answer: c) -4

Explanation:

Get the variables on one side of 3x+y=-2x+8 and the constants on another side:

3x+y=-2x+8

(3x+y)+2x=(-2x+8)+2x

5x+y=8

Now, multiply 5x+y=8 by -2:

-2(5x+y=8)

-10x-2y=-16

Add this equation to -3x+2y=-10:

(-10x-2y=-16)+(-3x+2y=-10)

-13x=-26

x=2

Plug x=2 into -3x+2y=-10:

-3(2)+2y=-10

-6+2y=-10

2y=-4

y=-2

Therefore, (2, -2) is the solution to the system of equations, so xy=(2)(-2)=-4