Thursday, 6 December 2012

inequality - Proving sumlimitsnk=1frac1sqrtkgesqrtn with induction



I am just starting out learning mathematical induction and I got this homework question to prove with induction but I am not managing.



nk=11kn




Perhaps someone can help me out I don't understand how to move forward from here:
n+1k=11k+1n+1n+1


proof and explanation would greatly be appreciated :)
Thanks :)



EDIT sorry meant GE not = fixed :)


Answer



If you wanted to prove that
nk=11kn,


that I can do. It is clear for n=1 (since we have equality then), so that it suffices to verify that
n+1k=11kn+1

but this is equivalent to
nk=11k+1n+1n+1 


and again equivalent to
nk=1n+1k+1n+1

so we only need to prove the last statement now, using induction hypothesis. Since
nk=11kn,

we have
nk=1n+1kn+1nnn=n.

Adding the 1's on both sides we get what we wanted.



Hope that helps,


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