Saturday, 24 October 2015

elementary number theory - Proof that n!>3n for nge4 using the Principle of Mathematical Induction


Use induction to prove that n!>3n for n4.




I have done the base case and got both sides being equal to 24>12 for n=4.
However, when doing the inductive step I can't seem to find the right form to match the expression on the right hand side.




So far I have:



Need to show: (n+1)!>3(n+1).



When doing the inductive step:



(n+1)!=(n+1)n!



we know that n! is larger than 3n, then




(n+1)n!>(n+1)3n.



Here is where I don't know what to do next, could anyone shed some insight on how to continue after this part? Thanks.

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