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?
问题描述：
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?
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答
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