Question

若向量a与b不共线,a*b不等于0.且c=a-[(a*a)/(a*b)]b,a与c夹角为?

Answer 1

a*c＝a*[a-[(a*a)/(a*b)]b]＝a*a-[(a*a)/(a*b)]（a*b）＝0.a与c夹角为90°