tanα=3.求3sin^2α-sinαcosα+2
问题描述：
tanα=3.求3sin^2α-sinαcosα+2
答
tanα=3
sinα/cosα=3
sin^2α/cos^2α=9
(1-cos^2α)/cos^2α=9
1/cos^2α-1=9
cos^2α=1/10
3sinα^2-sinαcosα+2
=cos^2α(3tan^2α-tanα)+2
=1/10*(3*3^2-3) + 2
=12/5+2
=22/5