



 
George, I would begin by translating the center to the origin so that the arithmetic is less complicated: subtract (x, y) from the given points to get (X', Y') = (Xx, Yy) and (A',B') = (Ax, By). (After your computation you will add (x, y) to (A', B') to get the coordinates of (A,B).) Now find the angle the line joining the origin to (X',Y') makes with the xaxis. (The tangent of that angle is Y'/X', so the desired angle is arctan (Y'/X').) Add that angle to the given angle (taking care if either of the angles is below the xaxis and therefore negative) to get the angle the line from the origin to (A',B') makes with the xaxis; call it theta. Then A' = radius*cos(theta) and B' = radius*sin(theta). Chris  


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