若tan2次方α=1/2,求cos2α=?sin2α=?

若tan2次方α=1/2,求cos2α=?sin2α=?
若tan2次方α=1/2,求cos2α=?sin2α=?

若tan2次方α=1/2,求cos2α=?sin2α=?
sin2α=2√2/3 cos2α=1/3

题目都没没有表达清楚，叫人怎么做？？

(tanα)^2=1/2
tanα = 1/√2 or -1/√2
cos2α = 2(cosα)^2 -1
= 2(√2/3)^2 -1
= 4/9 - 1
= -5/9
(sin2α)^2 = 1-(cos2α)^2
= 1- 25/81
= 56/81
sin2α = 2√14/9 or -2√14/9