Points【图片】 and 【图片】 are any two arbitrary points in a plane figure. The projections of the velocities of these two points on line 【图片】are 【图片】and 【图片】, respectively. The projections of the accelerations of these two points on line【图片】 are 【图片】and 【图片】, respectively. Then we can get 【图片】and 【图片】.