求n^5/e^n当n趋向于无穷时的极限.

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求n^5/e^n当n趋向于无穷时的极限.
求n^5/e^n当n趋向于无穷时的极限.

求n^5/e^n当n趋向于无穷时的极限.
用罗比达法则,
极限n^5/e^n
=极限5n^4/e^n
=极限5*4n^3/e^n
=极限5*4*3n^2/e^n
=极限5*4*3*2n/e^n
=极限5*4*3*2/e^n
=0

先利用洛比达法则求函数x^5/e^x的极限(x趋于正无穷) limx^5/e^x=5x^4/e^x=lim20x^3/e^x
=lim60x^2/e^x=lim120x/e6x=lim120/e^x=0 故由归结原则得limn^5/e^n=0