sin1x+sin2x+sin3x+sin4x+…+sinnx…一直加下去等于多少?

题目

sin1x+sin2x+sin3x+sin4x+…+sinnx…一直加下去等于多少?

答案

sinX乘以sin(X/2)=1/2（cos(x+x/2)-cos(x-x/2)）sin2X乘以sin(X/2)=1/2（cos(2x+x/2)-cos(2x-x/2)）sin3X乘以sin(X/2)=1/2（cos(3x+x/2)-cos(3x-x/2)）.sinNX乘以1/2sin(X/2)=1/2（cos(Nx+x/2)-cos(Nx-x/2)）发现上...