通分+注意tanx =sinx/cosx
limx→0(1/sinX)-(1/tanX)
=limx→0(1/sinX)-cosx/sinx
=limx→0 (1-cosx)/sinx
等价无穷小替换
x->0
1-cosx~x^2/2
sinx~x
所以极限
=limx→0 x^2/2x
=limx→0 x/2
=0
通分+注意tanx =sinx/cosx
limx→0(1/sinX)-(1/tanX)
=limx→0(1/sinX)-cosx/sinx
=limx→0 (1-cosx)/sinx
等价无穷小替换
x->0
1-cosx~x^2/2
sinx~x
所以极限
=limx→0 x^2/2x
=limx→0 x/2
=0