# [SOLVED] converting polar equations to rectangular equations

• Apr 7th 2010, 02:00 PM
satis
[SOLVED] converting polar equations to rectangular equations
I'm pretty stuck here.. any assistance would be helpful

given $\displaystyle r=3cos\Theta$, convert to rectangular form

I know that $\displaystyle r^2 = x^2 + y^2$, so I could square both sides

$\displaystyle r^2 = (3cos\Theta)^2$
$\displaystyle x^2 +y^2 = (3cos\Theta)^2$

But at that point I'm stuck. I have the answer from the back of the book, but can't work out how to complete the conversion.
• Apr 7th 2010, 02:21 PM
skeeter
Quote:

Originally Posted by satis
I'm pretty stuck here.. any assistance would be helpful

given $\displaystyle r=3cos\Theta$, convert to rectangular form

I know that $\displaystyle r^2 = x^2 + y^2$, so I could square both sides

$\displaystyle r^2 = (3cos\Theta)^2$
$\displaystyle x^2 +y^2 = (3cos\Theta)^2$

But at that point I'm stuck. I have the answer from the back of the book, but can't work out how to complete the conversion.

$\displaystyle r = 3\cos{\theta}$

multiply both sides by $\displaystyle r$ ...

$\displaystyle r^2 = 3r\cos{\theta}$

$\displaystyle x^2+y^2 = 3x$
• Apr 7th 2010, 02:22 PM
satis
ah! of course. Thanks a lot.