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johnnywang
just want to point out it's not quite right. You need to first find the polar angle for the original point (x,y), then add the $angle to that for the new polar angle.
<P>
<b>Updated</b>. I'm only refering to the geometric meaning. There is a formula: multiplying by the rotation matrix given by ((cos, -sin),(sin, cos)) (not perl notation!)
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