三道极限的题目
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(1) 原式 = lim<x→+∞>{[1+2/(x-1)]^[(x-1)/2]}^[2x/(x-1)]
= e^lim<x→+∞>2x/(x-1) = e^lim<x→+∞>2/(1-1/x) = e^2
(2) 原式 = lim<x→∞>[(1-1/x^2)^(-x^2)]^(-x/x^2)
= e^lim<x→∞>-1/x = e^0 = 1.
(3) 原式 = lim<x→∞>[(x-a+3a)/(x-a)]^x
= lim<x→∞>{[1+3a/(x-a)]^[(x-a)/(3a)]}^[3ax/(x-a)]
= e^lim<x→∞>3ax/(x-a) = e^lim<x→∞>3a/(1-a/x)
= e^(3a) = 8, 3a = ln8 = 3ln2, a = ln2.
= e^lim<x→+∞>2x/(x-1) = e^lim<x→+∞>2/(1-1/x) = e^2
(2) 原式 = lim<x→∞>[(1-1/x^2)^(-x^2)]^(-x/x^2)
= e^lim<x→∞>-1/x = e^0 = 1.
(3) 原式 = lim<x→∞>[(x-a+3a)/(x-a)]^x
= lim<x→∞>{[1+3a/(x-a)]^[(x-a)/(3a)]}^[3ax/(x-a)]
= e^lim<x→∞>3ax/(x-a) = e^lim<x→∞>3a/(1-a/x)
= e^(3a) = 8, 3a = ln8 = 3ln2, a = ln2.
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