第一题利用等价无穷小法则
lim(x→0)[tan(2x+x^3)/sin(x-x^2)]
=lim(x→0)[(2x+x^3)/(x-x^2)]=0
第二题分子分母同时除以x
lim(x→0)[(x-sinx)/(x+sinx)]
=lim(x→0)[(1-（sinx/x))/(1+(sinx/x))]然后利用等价无穷小
=lim(x→0)[(1-1)/(1+1）]=0