已知tana=2,求34sin^2a+12+sin2a

题目

已知tana=2,求34sin^2a+12+sin2a
写错了，是34sin^2a+12+sin2a

答案

3/(4sin^2a+12+sin2a)=3(sin^2a+cos^2a)/(4sin^2a+sin^2a+cos^2a2+2sinacosa)=3(sin^2a+cos^2a)/(5sin^2a+cos^2a2+2sinacosa)分子分母同时除以cos^2a=3(sin^2a/cos^2a+cos^2a/cos^2a)/(5sin^2a/cos^2a+cos^2a/cos...