若tanα =3,求3sin^a-sinacosa+2=?
问题描述:
若tanα =3,求3sin^a-sinacosa+2=?
答
应该是3sinα^2吧tanα=3sinα/cosα=3sin^2α/cos^2α=9(1-cos^2α)/cos^2α=91/cos^2α-1=9cos^2α = 1/103sinα^2-sinαcosα+2 = cos^2α(3tan^2α-tanα)+2= 1/10*(3*3^2-3) + 2= 12/5+2= 22/5