Rectangular and polar

A point can be described in two ways. In rectangular coordinates, $P(x,\ y)$: $\displaystyle x$ across and $\displaystyle y$ up. In polar coordinates, $P(r,\ \theta)$: a distance $\displaystyle r$ from the origin and an angle $\displaystyle \theta$. To go from rectangular to polar, $r=\sqrt{x^{2}+y^{2}}$, and $\displaystyle \theta$ is the inverse tangent of $\displaystyle y/x$. To go back, $x=r\cos\theta$, and $\displaystyle y = r\sin\theta$. The calculator does both conversions and also stores the results: $\displaystyle r$ or $\displaystyle x$ in memory X, and $\displaystyle \theta$ or $\displaystyle y$ in memory Y.

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