有些三角题若用三角法求解则解法冗长 ,教材中的两角差的余弦公式是利用单位圆上的点的坐标给予证明的 .这给予我们启示 ,若有 f( cosα,sinα) =0 ,注意到 sin2α +cos2 α=1 ,我们可以把点 P( cosα,sinα)看成单位圆 x2 + y2 =1与曲线 f ( x,y) =0的交点 .因此某些三角题可 Some trigonometric problems use the trigonometry method to solve the lengthy solution, the two-corner cosine formula in the textbook is proved by the coordinates of the points on the unit circle. This gives us inspiration, if there is f( cosα,sinα) =0 , Note that sin2α + cos2 α=1, we can think of the point P (cosα, sinα) as the intersection of the unit circle x2 + y2 =1 and the curve f (x, y) =0. So some triangular problems can be