题目应该是tana=3吧2sin²α-3sinαcosα-1=2sin²α-3sinαcosα-（sin^2a+cos^2a）=sin^2a-3sinacosa-cos^2a=(sin^2a-3sinacosa-cos^2a)/(sin^2a+cos^2a)=(tan^2a-3tana-1)/(tan^2a+1)=(9-9-1)/(9+1)=-1/1...