三角函数公式

高等数学中经常用到的三角函数公式：

sin(x)+sin(y)=2sin(x+y/2)*cos(x-y/2);

sin(x)-sin(y)=2cos(x+y/2)*sin(x-y/2);

cos(x)+cos(y)=2cos(x+y/2)*cos(x-y/2);

cos(x)-cos(y)=-2sin(x+y/2)*sin(x-y/2);

sin(x+y)=sinx*cosy+cosx*siny;

sin(x-y)=sinx*cosy-cosx*siny;

cos(x+y)=cosx*cosy-sinx*siny;

cos(x-y)=cosx*cosy+sinx*siny;

tan(x+y)=(tanx+tany)/(1-tanx*tany);

cot(x+y)=(cotx*coty-1)/(cotx+coty);