a.b都为锐角,cos(a+b)=-11/14,cosa=1/7,则角b=?
问题描述:
a.b都为锐角,cos(a+b)=-11/14,cosa=1/7,则角b=?
答
sin(a+b)=5√3/14 sina=4√3/7
sinb=sin(a+b-a)=sin(a+b)cosa-cos(a+b)sina =√3/2
b=π/3