# Question #3177e

Nov 22, 2014

The line perpendicular to $3 x + 9 y = 0$ has the equation $y = 3 x$

$3 x + 9 y = 0$

Putting this into the form $y = m x + c$ we get:

$y = \frac{- x}{3}$

So $m = - \frac{1}{3}$

If two lines A and B are perpendicular then gradient of

So gradient of B $\frac{- 1}{- \frac{1}{3}} = 3$
So the perpendicular line has the equation $y = 3 x$