根号下2/4sin(π/4-x)+根号下6/4cos(π/4-x)

问题描述:

根号下2/4sin(π/4-x)+根号下6/4cos(π/4-x)

√2/4 sin(π/4-x)+√6/4 cos(π/4-x)=√2/2 [1/2 sin(π/4-x)+√3/2 cos(π/4-x)]=√2/2 [cosπ/3 sin(π/4-x)+sinπ/3 cos(π/4-x)]=√2/2sin(π/4-x+π/3)=√2/2sin(7π/12-x)=√2/2sin(π/2+π...倒数第二步怎么来的啊7π/12=6π/12+π/12=π/2+π/12然后再用诱导公式sin(π/2+a)=cosa