Math Help - trigonometry recatangular to polar form

1. trigonometry recatangular to polar form

I am trying to convert this rectangular equation to polar form.

$
(x-2)^2 + y^2 = 4
$

$
(r cos \theta - 2)^2 + r (sin \theta)^2 = 4
$

I get lost after this,

2. Originally Posted by robasc
I am trying to convert this rectangular equation to polar form.

$
(x-2)^2 + y^2 = 4
$

$
(r cos \theta - 2)^2 + ( {\color{red}r} sin \theta)^2 = 4
$

I get lost after this,

Note the typo I've fixed (in red). Now expand $(r \cos \theta - 2)^2$ and simplify the resulting expression (the Pythagorean Identity is your friend).