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Complex numbers

11ejθ=12(1+jcot(θ2)\displaystyle\frac{1}{1-e^{j\theta}}=\frac{1}{2}(1+jcot(\frac{\theta}{2})
Need help on this question, i've tried to rationalize after converting to mod arg form and I got;
1cos(θ)+jsin(θ)2(1cos(θ)\displaystyle\frac{1-cos(\theta)+jsin(\theta)}{2(1-cos(\theta)}
But I'm pretty sure I'm not going the right way about it because of the half theta on the RHS. Which leads me to thinking it's something to do with the identity α+1=2cos(θ2)ejθ2\alpha + 1=2cos(\frac{\theta}{2})e^{j\frac{\theta}{2}}
and the other one. but how do I get it in that form?

Thanks in advance.
(edited 10 years ago)
Original post by ChildishHambino
11ejθ=12(1+jcotθ2)\displaystyle\frac{1}{1-e^{j\theta}}=\frac{1}{2}\left(1+j\cot \tfrac{\theta}{2}\right)
Need help on this question, i've tried to rationalize after converting to mod arg form and I got;
1cos(θ)+jsin(θ)2(1cos(θ)\displaystyle\frac{1-cos(\theta)+jsin(\theta)}{2(1-cos(\theta)}
But I'm pretty sure I'm not going the right way about it because of the half theta on the RHS. Which leads me to thinking it's something to do with the identity α+1=2cos(θ2)ejθ2\alpha + 1 = 2\cos \left(\frac{\theta}{2}\right)e^{j\frac{\theta}{2}}
and the other one. but how do I get it in that form?

Thanks in advance.

lol jj u wot m8

11eix=1cosx+isinx(1cosx)2+sin2x=1cosx+isinx2(1cosx)\displaystyle \frac{1}{1-e^{ix}} = \frac{1-\cos x + i \sin x}{(1-\cos x)^2 + \sin^2 x} = \frac{1-\cos x + i \sin x}{2(1-\cos x)}

Divide top by 1cosx1 - \cos x and recall what sinx1cosx\dfrac{\sin x}{1-\cos x} is.
(edited 10 years ago)
Original post by Felix Felicis
lol jj u wot m8

11eix=1cosx+isinx(1cosx)2+sin2x=1cosx+isinx2(1cosx)\displaystyle \frac{1}{1-e^{ix}} = \frac{1-\cos x + i \sin x}{(1-\cos x)^2 + \sin^2 x} = \frac{1-\cos x + i \sin x}{2(1-\cos x)}

Divide top and bottom by 1cosx1 - \cos x and recall what sinx1cosx\dfrac{\sin x}{1-\cos x} is.

MEI has got me in its grasp :/. And sinx/1-cosx? I'm guessing its something like tan(x/2) and thanks :smile:
Original post by ChildishHambino
MEI has got me in its grasp :/. And sinx/1-cosx? I'm guessing its something like tan(x/2) and thanks :smile:

Not quite, write sinx1cosx=2sinx2cosx21(cos2x2sin2x2)\displaystyle \frac{\sin x}{1 - \cos x} = \frac{2\sin{\frac{x}{2}} \cos{\frac{x}{2}}}{1 - \left(\cos^2 \frac{x}{2} - \sin^2 \frac{x}{2}\right)}.
Original post by Felix Felicis
Not quite, write sinx1cosx=2sinx2cosx21(cos2x2sin2x2)\displaystyle \frac{\sin x}{1 - \cos x} = \frac{2\sin{\frac{x}{2}} \cos{\frac{x}{2}}}{1 - \left(\cos^2 \frac{x}{2} - \sin^2 \frac{x}{2}\right)}.

Yeah haha just worked it out thanks :smile:

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