依题意ab=|a||b|cos60°=3，（1）向量cd=(3a+5b)(ma-3b)=3ma^2+(5m-9)ab-15b^2=27m+3(5m-9)-60=42m-87=0,m=29/14.(2)c,d共线，<==>m/3=-3/5,<==>m=-9/5.
