- #1
Math Monster
- 11
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Homework Statement
Show that the formula:
∫_0^∞ (s^a-1)/(s-1) ds = -pi cot (a pi)
may be calculated by considering an analytical branch of function:
f(z) = z^(a-1) / (z-1)
and integrating along a contour consisting of:
a) a circle radius R, centred at (0,0)
b) with a branch cut running from (0,0) to R above and below the x-axis
c) circular contours around singularity (0,0) and (1,0)
when R→∞
I have attempted to substitute s=Re^i alpha z, and I believe the integral around (a) → 0 as R → infinity but i can't really make sense of it all!
Please help and thanks in advance!
Show that the formula:
∫_0^∞ (s^a-1)/(s-1) ds = -pi cot (a pi)
may be calculated by considering an analytical branch of function:
f(z) = z^(a-1) / (z-1)
and integrating along a contour consisting of:
a) a circle radius R, centred at (0,0)
b) with a branch cut running from (0,0) to R above and below the x-axis
c) circular contours around singularity (0,0) and (1,0)
when R→∞
I have attempted to substitute s=Re^i alpha z, and I believe the integral around (a) → 0 as R → infinity but i can't really make sense of it all!
Please help and thanks in advance!