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Math 411: Honours Complex Variables - University of Alberta

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84 CHAPTER 12. THE RESIDUE THEOREM AND APPLICATIONS<br />

Imz<br />

iR<br />

ir<br />

Cr<br />

CR<br />

r R<br />

Rez<br />

We note that f(z) = e ixz z α−1 is holomorphic inside the blue contour. Cauchy’s<br />

Integral Theorem thus implies that<br />

� R �<br />

0 = f(t)dt+<br />

r<br />

CR<br />

� r �<br />

f +i f(it) dt+ f.<br />

R Cr<br />

Since α < 1, we see on using Problem 12.3 (a) that<br />

��<br />

�<br />

�<br />

�<br />

CR<br />

�<br />

�<br />

f�<br />

� ≤<br />

� π/2<br />

0<br />

≤ R α−1<br />

� π/2<br />

e −xRsinθ R α−1 R dθ<br />

Likewise, since α > 0, we see that<br />

Hence<br />

� ∞<br />

0<br />

as claimed.<br />

0<br />

��<br />

�<br />

�<br />

�<br />

Cr<br />

f(t)dt = −<br />

�<br />

�<br />

f�<br />

�<br />

e −2xRθ/π α−1 π �<br />

−xR<br />

R dθ = R 1−e<br />

2x<br />

� → 0.<br />

R→∞<br />

� −xr π 1−e<br />

≤ rα<br />

2x r<br />

� 0<br />

∞<br />

f(it) idt = i α<br />

�<br />

� ∞<br />

0<br />

→<br />

r→0 0.<br />

e −xt t α−1 dt = iαΓ(α) xα ,

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