错了.(1 -sinx)/cosx = [ 1 -tan (x/2) ] / [ 1 +tan (x/2) ].应该是：(1 -cos x) /sin x = tan (x/2),或：sin x /(1 +cos x) = tan (x/2).= = = = = = = = =1.(1 -cos x) /sin x = tan (x/2).证明：因为 cos x =1 -...