Question

在△ABC中,角A,B,C所对的边分别为a,b,c,向量m=[cos(A/2),sin(A/2)],n=[-cos(B/

Answer 1

1.mn=1/2 [cos(A/2),sin(A/2)]*[-cos(B/2),sin(B/2)]=-cos(A/2)cos(B/2)+sin(A/2)sin(B/2)=-cos C=60度

2.根号3)/4