利用二倍角公式sin x=2sin x/2 cos x/21+cos x=2(cos x/2)^21-cos x=2(sin x/2)^2代入(1+sinx+cosx) / (1+sinx-cosx)=（2(cos x/2)^2+2sin x/2 cos x/2）/(2(sin x/2)^2+2sin x/2 cos x/2) 上下约去2（cos x/2+sin x...