- #1
EC92
- 3
- 0
Homework Statement
I have the following problem:
Compute
[itex] \operatorname{Re} \int _\gamma \frac{\sqrt{z}}{z+1} dz, [/itex]
where [itex] \gamma [/itex] is the quarter-circle [itex] \{ z: |z|=1, \operatorname{Re}z \geq 0 , \operatorname{Im} z \geq 0 \} [/itex] oriented from 1 to [itex]i[/itex], and [itex] \sqrt{z} [/itex] denotes the principal branch.
Homework Equations
The Attempt at a Solution
I've been trying to solve this using the complex analog of the 2nd Fundamental Theorem of Calculus. Substituting [itex] u = \sqrt{z} [/itex] and using partial fractions, I get
[itex] \int_\delta 2 - \frac{i}{u+i} + \frac{i}{u-i} du [/itex]
where delta is the eighth-circle from 1 to [itex] e^{i\pi /4} [/itex]
This is equal to
[itex] [2u - i \log(u+i) + i\log (u-i)]_{u=1} ^{u=e^{i\pi/4}} [/itex],
and the real part is then
[itex] [\operatorname{Re} u + \operatorname{Arg}(u+i) -\operatorname{Arg}(u-i)]_{u=1} ^{u = e^{i \pi /4}} [/itex]
However, the arguments at [itex] u=e^{i\pi /4} [/itex] do not come out to nice forms. I am wondering if my approach is even correct, and if there's a better way to solve problems of this type.
Thanks.
[Mathematica says the value is approximately -0.584].