为什么sin(a+b)-sina=2sin(b/2)cos(a+b/2)
问题描述:
为什么sin(a+b)-sina=2sin(b/2)cos(a+b/2)
答
a+b=a+b/2+b/2,a=a+b/2-b/2sin(a+b)-sina=sin[(a+b/2)+(b/2)]-sin[(a+b/2)-(b/2)]展开=sin(a+b/2)*cosb/2+cos(a+b/2)*sinb/2-[sin(a+b/2)*cosb/2-cos(a+b/2)*sinb/2]=2sin(b/2)cos(a+b/2)...