sinx<x<tanx,即cosx< sInx <1 上式对于-<x<0也成立.当0<x<时, 2 x 0<c0sx-1=1-c0sx=2sin24<2( 2 lim=0, . lim(1-cos x)=0, x→>02 x→>0 lim cos x=1,又:lim1=1,∴lim sInx x→>0 x→0 →0sin x  x  tan x, 1, sin cos   x x 即 x 0 . 2 上式对于   也成立  − x , 2 当 0 时   x  0  cos x − 1 = 1 − cos x 2 2sin2 x = 2 ) 2 2( x  , 2 2 x = 0, 2 lim 2 0 = → x x  lim(1 cos ) 0, 0  − = → x x limcos 1, 0  = → x x lim1 1, 0 = x→ 又 1. sin lim 0  = → x x x