最后结果正确，中间红框内书写错误。应为：
lim[2ln(1-x/2+x^2/3)+x]/x^2
= lim{2ln[1-(x/2-x^2/3)]+x}/x^2
= lim{2 [-(x/2-x^2/3) - (1/2)(x/2-x^2/3)^2 -...] + x} / x^2
= lim{2 [-x/2 + x^2/3 - (1/2)(x/2)^2 +o(x^2)] + x} / x^2
= lim{2 [-1/2 + x/3 - (1/2)(x/4) +o(x^2)] + 1} / x
= lim2 [ x/3 - (1/8)x +o(x^2)] / x = 2(1/3 - 1/8)
