Thinking: Let the intersection of a circle and a straight line L: Y = 2 be W, the vertical foot from point P to straight line L be S, and extend the straight line L at the intersection of OP to r,. Then the coordinate of point P is (WS, 2-PS), so it is easy to prove that ws = WQ, ps = rsctgWOP, where QW=2, OQ, WQ, ctgWOP can be expressed by an expression containing x and y, so that the function expression 2-ps = f (ws) can be obtained.