Question

How do you solve the system `x + y = 14` and `-x + y = 16`?

Answer 1

`color(green)((x,y)=(-1,15))`

Explanation:

Given
[1]`color(white)("XXX")x+y=14`
[2]`color(white)("XXX")-x+y=16`

Adding [1] and [2] gives
[3]`color(white)("XXX")2y=30color(white)("XX")rarrcolor(white)("XX")y=15`

Subtracting [2] from [1] gives
[4]`color(white)("XXX")2x=-2color(white)("XX")rarrcolor(white)("XX")x=-1`