Question

在三角形ABC中，D是BC的中点，E是DC的中点，F是EC的中点，若AB的向量=a，AC的向量=b，则AF的向量=()A

Answer 1

AF=AB+BF =AB+7/8*BC =AB+7/8*(AC-AB) =AB+7/8*AC-7/8*AB =1/8*AB+7/8*AC =1/8*a+7/8*b .