Saturday, 27 January 2018

calculus - Limit as n goes to infinity of a limit involving factorials and exponents



limn=3((n+1)!)(n1)3n+(n!)n2



I'm stuck with this limit. I managed to rewrite it to the following form: 3n33n(n+1)!+n2(n+1)

but I don't know how to further simplify it. To me it seems like this goes to 0 because 3n grows faster than any other term in the function, but wolfram alpha tells me it's 3.


Answer




Divide the top and bottom by n!:
limn3((n+1)!)(n1)3n+(n!)n2=limn3(n+1)(n1)3nn!+n2=limn3n23n2=limn33n2=3


The thing is that n! grows way faster than 3n once n>3.


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