Question

How do you solve `x-y=9` and `2x+2y=2`?

Answer 1

• Substitute one value by using the other
• Set equation 1 into equation 2
• Solve like a normal equation.

Explanation:

`1: x - y = 9`
`2: 2x + 2y = 2`

Rewrite equation 1:
`x = 9 + y`

Put `9+y` instead of `x` in equation 2:
`2(9+y) + 2y = 2`

Solve like normal:
`18 + 2y + 2y = 2`
#4y = -16

Divide both sides by 4:
`y = -4`

Put this value into equation 1:
`x - (-4) = 9`
`x + 4 = 9`
`x = 9 - 4`
`x = 5`

To sum it up; `x = 5` and `y = (-4)`