Question

8x-3y = -21, 3x + y = -10; Prove: x = -3

Answer 1

We can prove x = -3 by plugging in 3 for x for each equation and show that each equation yields the same:

8x - 3y = -21

`8(-3)-3y=-21\\-24-3y=-21\\-3y=3\\y=-1`

3x + y = -10

`3(-3)+y=-10\\-9+y=-10\\y=-1`

Because we plugged in x for each equation and got the same result for y, this proves that x = -3 is a solution to the system of equations.