## Functions Modeling Change: A Preparation for Calculus, 5th Edition

$$x^2+y^2=6x$$
We know the following: $$r=\sqrt{x^2+y^2} \\ cos\theta = \frac{x}{\sqrt{x^2+y^2} }$$ Thus: $$\sqrt{x^2+y^2} = \frac{6x}{\sqrt{x^2+y^2} } \\ x^2+y^2=6x$$