题目

已知a∈(0,π/2),sin(a+π/3)=3/5,则sina=?
如果能顺便帮我总结一下以后碰到这种题型该怎么做就更好了

提问时间：2020-10-04

答案

a∈(0,π/2),
a+π/3∈(π/3,5π/6),
cos(a+π/3)=-4/5
sina
=sin(a+π/3-π/3)
=sin(a+π/3)cosπ/3-cos(a+π/3)sinπ/3
=3/5*1/2+4/5*√3/2
=3/10+2√3/5
sin(a+π/3)=3/5