求：极限的证明过程 (n）时,lim1/2^2=0 ；(x→2）lim(x+3)=5 ；(x→∞)lim1/x=0

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=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