X→0时,arctanx~X
变量替换,令arctanx=y,x=tany,x趋于0时,y趋于0,因此
lim arctanx/x
=lim y/tany
=lim ycosy/siny
=lim cosy/(siny/y)
=1.即arctanx~x
X→0时,arctanx~X
变量替换,令arctanx=y,x=tany,x趋于0时,y趋于0,因此
lim arctanx/x
=lim y/tany
=lim ycosy/siny
=lim cosy/(siny/y)
=1.即arctanx~x