What kind of article does this passage NOT belong to? A) An advertisement for medicine. B) An introduction to osteoarthritis. C) A science report from a health agency. D) A research paper of a professor.
【简答题】在△ABC中,满足 AB 与 AC 的夹角为60°,M是AB的中点, (1)若 | AB |=| AC | ,求向量 AB +2 AC 与 AB 的夹角的余弦值;. (2)若 | AB |=2,| BC |=2 3 ,点D在边AC上,且 AD =λ AC ,如果 MD ? AC =0 ,求λ的值.