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Homework Statement
Hi all, I am back with more questions. Thank you to those helped with my last assignment.
Question 1:
For |x| ≤ π, define a sequence of functions by:
Kn(x) = {n if -π/n ≤ x ≤ π/n, 0 otherwise} for natural numbers n. An earlier part of the question asked that I extend the function periodically. The question I need help on asks:
If f(x) is a Riemann integrable periodic function? R(T)?, then the limit as n approaches infinity, of the convolution (f * Kn)(x) = f(x) whenever f is continuous at x. (f * Kn)(x) denotes the convolution as a function of (x), not multiplied by (x).
We are to prove this statement directly using the Fundamental Theorem of Calculus.
Question 2:
Use the integral test for series to prove that Ʃ from k=1..n of 1/k is ≥ ln(n + 1) for all n≥1.
Homework Equations
The Attempt at a Solution
FIRST QUESTION: Instructor asked that we start by writing F(x) = ∫ from -π to x of f(t)dt. Lastly, we should not require the use of uniform continuity.
I seriously don't know where to start. I have written that much, and I've written out the convolution as an integral of f(y)Kn(x-y) dy, but I don't know where to go from there.
SECOND QUESTION: I have tried a few things: integral of 1/x from k to k+1 is ln|k+1| + ln|k| = ln|k+1|, which is good to see. Intuitively, I can understand this question, but I don't know what to write down or how to do it. The integral test tells us if the integral is finite, then the series converges. It does not state any equalities or inequalities; it is merely a test for convergence. I see how the integral test will help, but I don't know how to formally relate the test and the sum/inequality, since the integral test does not say anything about equality.
Any help would be much appreciated!