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I am trying to calculate input impedance of a multiple feedback low pass filter. What I need is the symbolic expression as simple as possible so that later I fill in the values and get the impedance itself:

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I assume that I am on right track in calculation, the thing is I can not go any further and simplify the equation more. Can someone please help with putting calculated V2 (down in the writings) into equation 2 and then put Vin into equation 1 and simplify it so that i1 will be removed?

P.S: I posted this question in electronics and math of stack exchange but they suggested to be posted in physics!

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Hi Sean - as I commented on your question on the math site, it sounds like you're just asking about simplifying an equation, in which case this question is off topic here. If that's not what you're asking about, I'd encourage you to clarify your question to make it clear what physical concept you're confused about. Once you can do that I'll be happy to reopen this. – David Zaslavsky♦ Feb 13 '12 at 7:40
With some editing, I think this could be a good question. Although it nominally might be a better fit for the EE site, a physics POV might be better. – nibot Feb 13 '12 at 7:57
@nibot maybe you can help Sean clarify what is being asked here, then. We can hash this out in Physics Chat if that would be best (although I'm signing off for the night now, I'll get back to this tomorrow). – David Zaslavsky♦ Feb 13 '12 at 8:25

closed as off topic by David Zaslavsky♦ Feb 13 '12 at 7:42

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