tan∠a=2,cos²∠a=?sin六次方∠a+cos六次方∠a=?

tana=2
1/(cosa)^2=1+(tana)^2=5
(cosa)^2=1/5 (sina)^2=4/5
sinacosa=tana*(cosa)^2=2*(1/5)=2/5
(sina)^6+(cosa)^6=[(sina)^2+(cosa)^2]*[(sina)^4-(sinacosa)^2+(cosa)^4]
=1*[(4/5)^2-(2/5)^2+(1/5)^2]
=13/25