Sunday, April 15, 2018

improper integrals - Convergence of inti0nftysin(t)/tgammamathrmdt




For what values of γ0 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<γ1. 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]1γ1cos(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=1tγ1.




This shows that the interval of convergence is (0,2).


No comments:

Post a Comment

analysis - Injection, making bijection

I have injection f:AB and I want to get bijection. Can I just resting codomain to f(A)? I know that every function i...