给出下列函数①y=xcosx②y=sin2x③y=x2-x④y=ex-e-x,其中是奇函数的是( )
— Tom, don't forget to return this dictionary by Saturday.
—_________ .
已知向量a,b,满足|a|=2,、|b|=3,|2a+b|=37,则a与b的夹角为( )