tan(a-4/π)=(tana-tanπ/4)/(1+tanatanπ/4)=(tana-1)/(1+tana)=2,所以tana=-3而1/(2sinacosa+cos^2a)=(sin^2a+cos^2a)/(2sinacosa+cos^2a) 分子分母同时除以cos^2a得=（tan^2a+1)/(2tana+1)=(9+1)/(1-6)=-2...