Question:
Prove 1+14+19+⋯+1n2≤2−1n, for all natural n
My attempt:
Base Case: n=1 is true:
I.H: Suppose 1+14+19+⋯+1k2≤2−1k, for some natural k.
Now we prove true for n=k+1
1+14+⋯+1k2+1(k+1)2≤2−1k+1(k+1)2, by induction hypothesis
Now how do I show that 2−1k+1(k+1)2≤2−1(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<1k−1k+1 or
1(k+1)2<1k(k+1),
which is obvious.
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