## Precalculus (6th Edition) Blitzer

In converting $r=5$ from a polar equation to a rectangular equation, square both sides of the equation such that ${{r}^{2}}$ gets replaced with ${{x}^{2}}+{{y}^{2}}$.
Consider the given polar equation, $r=5$ Squaring both sides of the equation we get, \begin{align} & {{r}^{2}}={{5}^{2}} \\ & =25 \end{align} Use, ${{r}^{2}}={{x}^{2}}+{{y}^{2}}$ Therefore, ${{x}^{2}}+{{y}^{2}}=25$ Hence, to convert $r=5$ from a polar equation to a rectangular equation, we will square both sides of the equation such that ${{r}^{2}}$ gets replaced with ${{x}^{2}}+{{y}^{2}}$.