## Precalculus (6th Edition) Blitzer

The rectangular equation is ${{x}^{2}}+{{y}^{2}}=x$.
Using ${{r}^{2}}={{x}^{2}}+{{y}^{2}}$ we will convert the polar equation to the rectangular equation. $x=r\cos \theta,y=r\sin \theta$ Therefore, \begin{align} & r=\cos \theta \\ & {{r}^{2}}=r\cos \theta \\ & {{x}^{2}}+{{y}^{2}}=r\cos \theta \\ & =x \end{align}