题目

(sinx-siny)/sin(x+y) = sin1/2(x-y)/sin1/2(x+y)
还有这个sec(π/4+α)sec(π/4-α)=2sec2α

提问时间：2021-01-02

答案

sinx=sin[(x+y)/2]cos[(x-y)/2]+cos[(x+y)/2]sin[(x-y)/2]siny=sin[(x+y)/2]cos[(x-y)/2]-cos[(x+y)/2]sin[(x-y)/2]sinx-siny=2cos[(x+y)/2]sin[(x-y)/2]sin(x+y)=2sin[(x+y)/2]cos[(x+y)/2]所以(sinx-siny)/sin(x+y...