lim(x→0)(1-cosx)/ln(1+x^2)
[洛必达法则]
=lim(x→0)sinx/[(2x)/(1+x^2)]
=lim(x→0)[sinx/2x]*(1+x^2)
[sinx和x是等价无穷小量]
=1/2*1
=1/2