For what values of γ≥0 does the improper integral ∫∞0sin(t)tγdt converge?
In order to avoid two "critical points" 0 and +∞ I've thought that it would be easier to test the convergence of the sum (is this coherent?):
∫10sin(t)tγdt+∫∞1sin(t)tγdt.
For the second integral, it converges if γ>1 (comparision) and also converges if 0<γ≤1. I'm stuck on proving the last part and the fact that the first integral converges for γ<2. Any help would be appreciated. Thanks in advance.
PD: I've checked the answers for this question but I would not like to solve this integral using (nπ,(n+1)π) intervals.
Answer
I was not going to answer, but the previous answers left me a bit anxious for t near ∞.
Integrate by parts to get
∫∞1sin(t)tγdt=−cos(t)tγ]∞1−γ∫∞1cos(t)tγ+1dt
and both converge at ∞ when γ>0.
Of course, as the previous answers have said
∫10sin(t)tγdt
converges when t<2 by comparison with ttγ=1tγ−1.
This shows that the interval of convergence is (0,2).
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