Question

How do you find the angle between the lines 3x+4y=12 and 4x-3y=12?

Answer 1

`90^@`

Explanation:

Rearrange so `3x+4y=12 =>4y=-3x+12=>y=-3/4x+3`

`4x-3y=12=>-3y=-4x+12=>y=4/3x-4`

the two gradients are `-3/4 and 4/3`

`-3/4xx4/3=-12/12=-1`

so they are perpendicular.