Question

已知cos（a+5π/12）=1/3，a为第三象限角，求sin（a-7π/12）的

要过程

Answer 1

解：sin（a-7π/12）=sin（a+5π/12-π）=-sin[π-（a+5π/12)]=sin[-（a+5π/12)]=-sin(a+5π/12)a为第三象限角,a+5π/12为第二象限角所以sin(a+5π/12)=根号下[1-（cos（a+5π/12））^2]=根号下8/9则sin（a-7π/12）=-sin(a+5π/12)=-根号下8/9