过圆x2+y2=r2上一点P0(x0,y0)作该圆的切线,只有一条,易知其方程为x0x+y0y=r2.当点P0(x0,y0)在圆x2+y2=r2外时,切线有两条,设切点分别为A、B,那么如何求直线AB的方程呢?本文借助一道高考题展开.例1(2013年山东高考题)过点(3,1)作圆(x-1)2+y2=1的两条切线,切点分别为A、B,则直线AB的方程为().(A)2x+y-3=0(B)2x-y-3=0(C)4x-y-3=0(D)4x+y-3=0 (1) P0 (x0, y0) is the tangent of the circle, only one is easy to know. The equation is x0x + y0y = r2. When the point P0 (x0, y0) is on the circle x2 + y2 = r2 When the outside, there are two tangent, set the cut point respectively A, B, then how to find a straight line AB equation? This article with a college entrance exam .Example 1 (Shandong 2013 entrance exam) (A) 2x + y-3 = 0 (B) 2x-y-1 The two tangent lines of the circle (x-1) 2 + y2 = 1 are tangent points A and B, respectively. 3 = 0 (C) 4x-y-3 = 0 (D) 4x + y-3 = 0