注 当0<x<时 0<1-COS x=1-cos X 2 Sin 2()2 lim(1-cos x)=0 ②0∞注： 当 2 0   x  时 0  1− cos x =1− cos x2 2sin 2 x = ( ) 2 2 2 x  22 x = lim(1 cos ) 0 0  − = → x x