已知tanα=4根号3,cos（α+β）=-11/14,α,β均为锐角,求cosβ的值
问题描述：
已知tanα=4根号3,cos（α+β）=-11/14,α,β均为锐角,求cosβ的值
答
{A = arctan(4*sqrt(3)),B = 1/3*Pi},{A = arctan(4*sqrt(3)),B = -arctan(39/71*sqrt(3))+Pi},{A = arctan(4*sqrt(3))-Pi,B = -2/3*Pi},{A = arctan(4*sqrt(3))-Pi,B = -arctan(39/71*sqrt(3))};所以cosB=0.5.