# Thread: [SOLVED] converting polar equations to rectangular equations

1. ## [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.

2. 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 $\displaystyle r$ ...

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

$\displaystyle x^2+y^2 = 3x$

3. ah! of course. Thanks a lot.