题目

sin(x+x1)-sinx=2sin(x1/2)cos(x+x1/2),这是怎么转换的?

提问时间：2020-12-07

答案

根据和差化积公式:sinA - sinB = 2cos((A+B)/2)sin((A-B)/2)
A = x + x1
B = x
(A + B)/2 = (2x + x1)/2 = x + x1/2
(A - B)/2 = (x + x1 - x)/2 = x1/2
因此,sin(x + x1) - sinx = 2sin(x1/2)cos(x + x1/2)