已知tan(α+π/4)=2,求cos2α+(3sin^2)α+tan2α的值

tan(a+π/4)=2
tanπ/4=1
所以tan(a+π/4)=(tana+1)/(1-tana)=2
tana+1=2-2tana
tana=1/3
所以sina/cosa=1/3
cosa=sina/3
(sina)^2+(cosa)^2=1
所以(sina)^2=9/10
tan2a=2tana/(1-tan^2a)=(2/3)/(8/9)=3/4
所以原式=1-2(sina)^2+3(sina)^2+tan2a
=1+(sina)^2+tan2a
=53/20