已知cos2α=-1/9,那么tan^2α×sin^2α的值为?

已知cos2α=-1/9,那么tan^2α×sin^2α的值为?
已知cos2α=-1/9,那么tan^2α×sin^2α的值为?

已知cos2α=-1/9,那么tan^2α×sin^2α的值为?
cos2a=2*(cos^2 a)-1=1-2*(sin^2 a)=-1/9 => cos^2 a=4/9; sin^2 a=5/9
(tan^2 a)*(sin^2 a)=(sin^4 a)/(cos^2 a)=25/36

sin 2;α+cos 2;α=1 所以cos 2;α=1-1/81=80/81 [cos(α-5π)tan(2π-α)/cos(3π/2 +α)]+tan 2;α =[-cosα(-tanα)]/sin