a,b为锐角,cos(a-b/2)=根号3/2,sin(a/2-b)=-1/2,求cos(a+b)
问题描述：
a,b为锐角,cos(a-b/2)=根号3/2,sin(a/2-b)=-1/2,求cos(a+b)
答
sin(a/2-b)=-1/2,a,b为锐角.cos(a/2-b)=√[1-sin^2(a/2-b)]=√3/2,sin[2(a/2-b)]=2*sin(a/2-b)*cos(a/2-b)=2*(-1/2)*√3/2=-√3/2.即,sin(a-2b)=-√3/2.cos(a-2b)=√[1-sin^2(a-2b)]=1/2.cos(a-b/2)=根号3/2,cos[2(a...