At this time, the length of arc rolling is 2-0 = 2. Assuming that the circle C (2, 1) and the X axis are tangent to Q (2 2,0), then the arc length PQ = 2. So the central angle PCQ = 2 radians. Using the property of tangent angle PQO = 1/2 × central angle PCQ, the slope of straight line PQ is k= -tan 1, so straight line PQ is y =-tan 1 (x-2), and C2 equation (x-2) 2+(y-6544) is established. And to solve y, we get y = 2sin2 (1) =1-cos 2, so x = y/(-tan1)+2 =-2sin1cos1+2 = 2-sin 2.

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