cos(A+B)=－11/14,
sin(A+B)=√[1-cos^2(A+B)]=5√3/14.
tan(A+B)=sin(A+B)/cos(A+B)=-5√3/11.
tanB=tan[(A+B)-A]=[tan(A+B)-tanA]/[1+tan(A+B)*tanA]=√3=tan60,
B=60度.