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1、原式=limx→1 [1/(x-1)(x-2)-2/(x-1)(x-3)]
=limx→1 [(x-3)-2(x-2)]/[(x-1)(x-2)(x-3)]
=limx→1 (1-x)/[(x-1)(x-2)(x-3)]
=limx→1 -1/[(x-2)(x-3)]
=-1/[(1-2)(1-3)]
=-1/2;
2、原式=limn→∞[n^3(2n+1)-n^2(2n^2-1)]/[(2n^2-1)(2n+1)]
=limn→∞ (n^3+n^2)/[(2n^2-1)(2n+1)]
=limn→∞ (1+1/n)/[(2-1/n^2)(2+1/n)]
=(1+0)/[(2-0)(2+0)]
=1/4。
=limx→1 [(x-3)-2(x-2)]/[(x-1)(x-2)(x-3)]
=limx→1 (1-x)/[(x-1)(x-2)(x-3)]
=limx→1 -1/[(x-2)(x-3)]
=-1/[(1-2)(1-3)]
=-1/2;
2、原式=limn→∞[n^3(2n+1)-n^2(2n^2-1)]/[(2n^2-1)(2n+1)]
=limn→∞ (n^3+n^2)/[(2n^2-1)(2n+1)]
=limn→∞ (1+1/n)/[(2-1/n^2)(2+1/n)]
=(1+0)/[(2-0)(2+0)]
=1/4。
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