过程省去limx-->0
(arctanx-sinx)/x*x*x
=[1/(1+x²)-cosx]/3x²(洛必达法则)
=[1-x²-1+2sin²(x/2)]/3x² (1/(1+x²)展开,cosx=1-2sin²x/2)
=(-x²+2*x²/4)/3x² (sinx/2和x/2为等价无穷小)
=(-1/2)/3
=-1/6
希望对你有所帮助