一个无穷小极限的疑问,为什么?

1个回答

左边=lim(x→0)(cos^2(x)-1)/(3x^2)*1/cos^2(x)
=lim(x→0)-sin^2(x)/(3x^2)*lim(x→0)1/cos^2(x)
=-1/3*1 (sinx~x)
=-1/3