If α, βϵ(0, π2) satisfy the following simultaneous equation 2 sin 2β=3 sin 2α and tanβ=3 tan α, then the value of (8 cos 2α) is ___
2.2 tan β1+tan2β=3. 2 tan α1+tan2 α⇒ 6 tan β1+9 tan2β=3 tan α1+tan α⇒1=7 tan2 α∴ cos2α=78