# Converting a polar equation to Cartesian form.

• Jul 9th 2011, 04:31 PM
weber
Converting a polar equation to Cartesian form.
I have been thinking about since morning, but didn't seen to find a way to even start to solve this:

Get the cartesian equation for the curve r=2*cos a , and make the graph of this curve

Can anyone help me? Thank you! (:
• Jul 9th 2011, 05:44 PM
skeeter
Re: Circumference
Quote:

Originally Posted by weber
I have been thinking about since morning, but didn't seen to find a way to even start to solve this:

Get the cartesian equation for the curve r=2*cos a , and make the graph of this curve

Can anyone help me? Thank you! (:

assuming you mean ...

$\displaystyle r = 2\cos{\theta}$ (instead of "a")

note that $\displaystyle x = r\cos{\theta}$ is one of your basic conversion equations.

rearranging ... $\displaystyle \frac{x}{r} = \cos{\theta}$

substitute $\displaystyle \frac{x}{r}$ for $\displaystyle \cos{\theta}$ in your original equation ...

$\displaystyle r = 2 \cdot \frac{x}{r}$

$\displaystyle r^2 = 2x$

also note that $\displaystyle r^2 = x^2+y^2$ ...

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

... and this would be the equation of what conic section?

Moderator edit: Excellent reply restored. Post #3 deleted.