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 $n\ge4 $.




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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