(a) When the circle is offset from the origin, the equation for the radius gets messy. In general, it will be the root of a quadratic equation in sine and cosine, not easily simplified. The Cartesian equation is easier to write.
Circle centered at (h, k) with radius r:
(x -h)^2 +(y -k)^2 = r^2
The given circle is ...
(x -2)^2 +(y -2)^2 = 16
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(b) When the circle is centered at the origin, the radius is a constant. The desired circle is most easily written in polar coordinates:
