√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