Question

How do you solve the system of linear equations `2x + y = 9` and `x - y = 3`?

Answer 1

`(x,y)=(4,1)`

Explanation:

Given:
[1]`color(white)("XXX")2x+y=9`
[2]`color(white)("XXX")x-y=3`

Add equations [1] and [2] to get
[3]`color(white)("XXX")3x=12`

Divide equation [3] by `3`
[4]`color(white)("XXX")x=4`

Substitute `4` for `x` in [2]
[5]`color(white)("XXX")4-y=3`

Think about it for a minute, then write
[6]`color(white)("XXX")y=1`