# Line equation : general understanding (Need ASAP help , exam tomorow)

• May 17th 2011, 10:14 AM
Sumaher4
Line equation : general understanding (Need ASAP help , exam tomorow)
Hello everyone ,

This is my first time here and because i dont have a lot of time left due of my examination tomorrow i will not spend much time on the grammar.

The point A has coordinates (7,7) and the line L has equation x+3y=8

(i) Find the equation of the line that passes through A and is perpendicular to L

I cant understand generaly what am i supposed to do here , plz provide me step by step with no "wordy" words , as simple as possible :p
• May 17th 2011, 10:28 AM
Quacky
Quote:

Originally Posted by Sumaher4
Hello everyone ,

This is my first time here and because i dont have a lot of time left due of my examination tomorrow i will not spend much time on the grammar.

The point A has coordinates (7,7) and the line L has equation x+3y=8

(i) Find the equation of the line that passes through A and is perpendicular to L

I cant understand generaly what am i supposed to do here , plz provide me step by step with no "wordy" words , as simple as possible :p

Start by rewriting your equation in y=mx+c form:

$\displaystyle 3y=-x+8$
$\displaystyle y=\frac{-1}{3}x+\frac{8}{3}$

The gradient of this line, I'll call it 'M', is $\displaystyle \frac{-1}{3}$

The gradient of the perpendicular line will be $\displaystyle \frac{-1}{M}$ - this is a general rule. Be careful with signs!

So what will the gradient of the perpendicular be?

Once you have it, you have a point and the gradient so forming an equation should be quite straightforward.