Elliptic Rotation

Leaves the Circle

$\begin{displaymath} x^2+y^2=1 \end{displaymath}$

invariant.

$\displaystyle x'$	$\textstyle =$	$\displaystyle x\cos\theta-y\sin\theta$
$\displaystyle y'$	$\textstyle =$	$\displaystyle x\sin\theta+y\sin\theta.$

See also Equiaffinity