题目

sin(x-20°)+cos(x+70°)+sin(x+20°)sec(70-x)=?
请问有何简便解法?

提问时间：2020-10-15

答案

sin(x-20°)+cos(x+70°)+sin(x+20°)sec(70-x)
=sin(x-20°)+sin(20°-x)+sin(x-20°)/cos(70°-x)
=sin(x-20°)-sin(x-20°)+sin(x-20°)/sin(x-20°)
=0+1
=1