知道Tan阿尔法等于三 4分之3Sin平方阿尔法加2分之1cos平方阿尔法 求值,

tana=3
3sin^2a/4+cos^2a/2
=1/4*(3sin^2a+2cos^2a)
=1/4*(3sin^2a+2cos^2a)/1
=1/4*(3sin^2a+2cos^2a)/(sin^2a+cos^2a)
=1/4*(3sin^2a/cos^2a+2cos^2a/cos^2a)/(sin^2a/cos^2a+cos^2a/cos^2a)
=1/4*(3tan^2a+2)/(tan^2a+1)
=1/4*(3*3^2+2)/(3^2+1)
=1/4*29/10
=29/40