tan（A－π）＝2tanA =2=>sinA = 2/√5 or - 2/√5 cosA =1/√5 or - 1/√5 (sinA)^2+sinA.cosA－2(cosA)^2= 2/5 + 2/5 - 2(1/5)=2/5
上面的答案中(sinA)^2=4/5，答案错误
