c//d 并且a.b不共线
c = ka+b ,d = a-b
=> 1/k = -1/1
=> k =-1
=>c = -a +b ,d=a-b
=> c = -d
=> c与d反向向量a加b和a-b之间有什么关系a+b与a-b的关系要看具体题目问了,单独不能考虑他们的关系