1–cosx的2次方等价于什么？
求解过程与结果如图所示
x->0
1-cosx =(1/2)x^2 +o(x^2)
(1-cosx)^2 =(1/4)x^4 +o(x^4)
lim(x->0) (1-cosx)^2/[x^2.(ln(1+x))^2]
=lim(x->0) (1-cosx)^2/x^4
=lim(x->0) (1/4)x^4/x^4
=1/4
等于sinx的2次方
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