cos(α-β/2)=-1/9,sin(α/2-β)=2/3,且π/2<α<π,0<β<π/2,求cos(α+β)的值
问题描述:
cos(α-β/2)=-1/9,sin(α/2-β)=2/3,且π/2<α<π,0<β<π/2,求cos(α+β)的值
答
cos(α-β/2)=-1/9
π/4