(1)tana=-1/2 1+tan²a=1/cos²a => cosa=-2/(5)^0.51-cos²a=sin²a => sina=1/(5)^0.5cosa-sina=-3/(5)^0.5(2)你确定是cos(pai/2+a)*(pai/2-a)*tan(pai+a)吗?没有漏?