cos(a-5π)tan(2π-a)/cos(3π/2+a)+tan^2a
=(-cosa)(-tana)/(-sina)+tan^2a
=-1+sin^2a/cos^2a
=-1+sin^2a/(1-sin^2a)
=-1+1/81/(1-1/81)
=-1+1/80
=-79/80已知sina=1/9,试求[cos(a-5π)tan(2π-a)]/[cos(3π/2+a)]+tan^2a的值"+tan^2a"是单独的 还有-1是哪来的(-cosa)(-tana)/(-sina)=sina/(-sina)=-1啊