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Complex integration

I need help integrating z+3i21z2+idz \int_{ |z+\frac{3i}{2}|} \frac{1}{z^2 +i} dz

So I have split it int

14λ12i(1zi1z+i)dz \frac{1}{4}\int_{\lambda} \frac{1}{2i} (\frac{1}{z-i} - \frac{1}{z+i})dz .

Now I'm unsure on how to parametrise the circle. I've been told to use zi=eit z - i = e^{it} but don't know how to replace it for z+iz+i.

Any help would be appreciated.
Original post by I Closed My Eyes
I need help integrating z+3i21z2+idz \int_{ |z+\frac{3i}{2}|} \frac{1}{z^2 +i} dz

So I have split it int

14λ12i(1zi1z+i)dz \frac{1}{4}\int_{\lambda} \frac{1}{2i} (\frac{1}{z-i} - \frac{1}{z+i})dz .

Now I'm unsure on how to parametrise the circle. I've been told to use zi=eit z - i = e^{it} but don't know how to replace it for z+iz+i.

Any help would be appreciated.


z+32i|z+\frac{3}{2}i| is a circle centred at z=32iz = -\frac{3}{2}i, but the radius is unclear. Are you sure you've written this correctly?

Also 1z2+i12i(1zi1z+i)\dfrac{1}{z^2+i} \neq \dfrac{1}{2i} \left( \dfrac{1}{z-i} - \dfrac{1}{z+i}\right)
Original post by RDKGames
z+32i|z+\frac{3}{2}i| is a circle centred at z=32iz = -\frac{3}{2}i, but the radius is unclear. Are you sure you've written this correctly?

Also 1z2+i12i(1zi1z+i)\dfrac{1}{z^2+i} \neq \dfrac{1}{2i} \left( \dfrac{1}{z-i} - \dfrac{1}{z+i}\right)


Forgot to mention the radius is r. I've tried splitting it into partial fractions.
Original post by I Closed My Eyes
Forgot to mention the radius is r. I've tried splitting it into partial fractions.


So the circle you are integrating along is z=32i+Reiθz = \frac{3}{2}i + Re^{i \theta} where θ\theta ranges from 0 to 2π2\pi.

You split that into partial fraction unsuccessfully... try again, or post your working out. Did you mean the fraction to be 1z2+1\dfrac{1}{z^2 + 1} instead?
Original post by RDKGames
So the circle you are integrating along is z=32i+Reiθz = \frac{3}{2}i + Re^{i \theta} where θ\theta ranges from 0 to 2π2\pi.

You split that into partial fraction unsuccessfully... try again, or post your working out. Did you mean the fraction to be 1z2+1\dfrac{1}{z^2 + 1} instead?


I found that the denominator z2+i=(z+i)(zi) z^2 + i = (z+i)(z-i) and then worked from there. I've decided to abandoned this method of mine, and would use your first line and the original fraction instead, since I got quite confused where I am integrating along.

Thank you
Original post by I Closed My Eyes
I found that the denominator z2+i=(z+i)(zi) z^2 + i = (z+i)(z-i) and then worked from there. I've decided to abandoned this method of mine, and would use your first line and the original fraction instead, since I got quite confused where I am integrating along.

Thank you


Have you not noticed that (z+i)(zi)=z2i2=z2+1z2+i(z+i)(z-i) = z^2 - i^2 = z^2 + 1 \neq z^2 + i ??

This is what I'm trying to sort out first... you keep saying z2+iz^2+i but factoring it as if it was z2+1z^2 + 1

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