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Something Dash

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I don't know if this is college level in other places, but around here it is.

And, English is not my Native language, so bear with my mistakes...

Anyway, my class is "Mathematical Models" AKA Control Systems. It is part of physics and math, anyways, while they give me a circuit kinda looking like THIS:

http://img94.echo.cx/img94/7059/circuito0gc.png

Well, that's the circuit. It is a Direct Current circuit, and i must find the "Mathematical Model" of this circuit,

As you can see, Entrada (Input) is V(t) and the output is VR(1). While i know acording Kirkchof laws,

V(t) = VR(1) + VR(2) or

V(t) = VR1 + VC

And in this case, the R1 and R2 Resistance are Equal, so R1 = R2 = R.

In order to write a math model i only need to express it on V(t) and VR(1) (Meaning, just the Output and Input) so i need to express VR(2) or VC in terms of VR1 ONLY and not V(t) cause that doesn't make sense.

This is when i go ballistic. While if the output is V(C) or VR(2) is piece of cake, here i cannot do nothing. All i can remember and investigate is that

IR1 = IR2 + IC

VR1/R = VR2/R + C . dVC/dt (Derivate) and while is in this position, i cannot put it into terms of VR1.

I KNOW i am missing something, but it was a long time ago when i saw physics... please, you are my last line of defense, i tried all my other exercises and this one is bothering me.

The meaning of doing that is finding the "Transference Function" i need to...

Laplace Output (In this circuit pic, Salida :D )

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Laplace Input (In this circuit, Entrada)

Thx beforehand, S'-