Question

How do you solve 3x+4y=0 and x-4y= -8?

Answer 1

`x=-2` and `y=3/2`

Explanation:

Given
[1]`color(white)("XXX")3x+4y=0`
[2]`color(white)("XXX")x-4y=-8`

Adding equations [1] and [2] together
[3]`color(white)("XXX")4x=-8`

Dividing both sides of [3] by `4`
[4]`color(white)("XXX")x=-2`

Substituting `(-2)` for `x` back in [2]
[5]`color(white)("XXX")(-2)-4y=-8`

`rarr`[6]`color(white)("XXX")-4y=-6`

`rar`r[7]`color(white)("XXX")y=3/2` ...or if you prefer a mixed number `y=1 1/2`