旋转法,是将图形旋转一个角度后使得分散的互不联系的条件有了联系,便于探索出解题的途径．例1 如图1,点P是等边△ABC内一点,且PA=3,PB= 5,PC=4,求∠APC的度数．分析将△APC绕点A按顺时针方向旋转60°至△ADB处,连接DP,得等边△ADP．所以DP=3,∠ADP=60°, 又因为DB=PC=4,PB=5, 而 32+42=52, 即△BDP中,有BD2+DP2=PB2．图1 The rotation method is to rotate the figure by an angle so that the conditions of the disjoint and unconnected are linked, and it is easy to explore ways to solve the problem. Example 1 As shown in Figure 1, point P is a point within the equator △ ABC, and PA = 3, PB = 5, PC = 4, find the degree of APC. Analysis △ APC rotates around point A in a clockwise direction by 60° to △ADB where DP is connected and is equidistantly △ADP. So DP=3, ∠ADP=60°, and because DB=PC=4, PB=5, and 32+42=52, that is, in BDDP, there is BD2+DP2=PB2. figure 1