Hello, I've recently encountered this problem: Prove these two equations are Orthoganal. x^2 + y^2 = r^2 | ax + by = 0 |

I get stuck after I differentiate both sides.

The left equation I get

2x + 2yy'= 0

= y' = -x/y

And the then the rightside

A + By' = 0

= y' = -a/b

I know I need to get rid of the A & B, but at the moment it's not clear to me. Any idea's on where to start? Thank you.