Wednesday, March 6, 2019

proof verification - Proving inequality 1+frac14+frac19+cdots+frac1n2le2frac1n using induction



Question:





Prove  1+14+19++1n221n, for all natural n




My attempt:



Base Case: n=1 is true:



I.H: Suppose 1+14+19++1k221k, for some natural k.




Now we prove true for n=k+1



1+14++1k2+1(k+1)221k+1(k+1)2, by induction hypothesis



Now how do I show that 21k+1(k+1)221(k+1) ?



Have I done everything correctly up until here?



If yes, how do I show this inequality is true?




Any help would be appreciated.


Answer



You are right!



We need to prove that:
1(k+1)2<1k1k+1 or
1(k+1)2<1k(k+1),
which is obvious.


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