Question

已知向量a.b不共线,c=ka+b,d=a-b,如果c平行于d,那么k=?c与d同向或反向?

Answer 1

if c//d and a.b不共线

c = ka+b and d = a-b

=> 1/k = -1/1

=> k =-1

k =-1

c = -a +b and d=a-b

=> c = -d

=> c与d:反向