求lim[ x^(n+1)-(n+1)x+n]/(x-1)^2 x-->1=lim(t->0) [ [ 1 + (n+1)t + (n+1)n/2t^2 + o(t^2)] -(n+1)-(n+1)t + n]/t^2?不懂

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求lim[ x^(n+1)-(n+1)x+n]/(x-1)^2 x-->1=lim(t->0) [ [ 1 + (n+1)t + (n+1)n/2t^2 + o(t^2)] -(n+1)-(n+1)t + n]/t^2?不懂

求lim[ x^(n+1)-(n+1)x+n]/(x-1)^2 x-->1=lim(t->0) [ [ 1 + (n+1)t + (n+1)n/2t^2 + o(t^2)] -(n+1)-(n+1)t + n]/t^2?不懂
求lim[ x^(n+1)-(n+1)x+n]/(x-1)^2 x-->1
=lim(t->0) [ [ 1 + (n+1)t + (n+1)n/2t^2 + o(t^2)] -(n+1)-(n+1)t + n]/t^2?不懂

求lim[ x^(n+1)-(n+1)x+n]/(x-1)^2 x-->1=lim(t->0) [ [ 1 + (n+1)t + (n+1)n/2t^2 + o(t^2)] -(n+1)-(n+1)t + n]/t^2?不懂
①令:x = 1+t (t->0)
lim(x->1) [ x^(n+1)-(n+1)x+n]/(x-1)^2
=lim(t->0) [ (1+t)^(n+1)-(n+1)(1+t) + n]/t^2
【二项式展开, o(t^2) 表示t^2的高阶无穷小量:(n+1)n(n-1)t^3/3! + ... + t^(n+1) 】
=lim(t->0) [ [ 1 + (n+1)t + (n+1)n/2t^2 + o(t^2)] -(n+1)-(n+1)t + n]/t^2
=(n+1)n/2
② 罗必塔法则:
lim(x->1) [ x^(n+1)-(n+1)x+n]/(x-1)^2
=lim(x->1) [(n+1)x^n -(n+1)]/2(x-1)
=lim(x->1) (n+1)nx^(n-1)/2
=n(n+1)/2