Solution: X 2+Y 2 =1(y ≤ 0) can be obtained from the curve equation, and its image is a semicircle below the X axis, as shown in the figure. The slope of PB is k 1= 1, and the slope of KC is 4/3 (according to the distance from the center of the circle to the straight line, it is equal to the radius of 65438+).