cos65π/6=cos(65π/6-10π)=cos(5π/6)=cos(π-π/6)=-cosπ/6=-√3/2 sin(-31π/4)=sin(-31π/4 8π)=sin(π/4)=√2/2 tancos65π/6=cos(65π/6-10π)什么意思 最后的√2/2 tan 为什么还要有tan呢？