Question: Symbolic solution

I tried posting this on a similar post but didn't get a response:

I'm trying a similar thing but the intermediate voltages (in my case Va, and Vb) are not being removed.  Here are my equations:

eq := Vo = K*(Vb-Vo), i3 = C3*Vb*s, Va-Vb = R3*i3, i2 = C2*s*(Vo-Va), Vi-Va = R1*i1, i3 = i1+i2
sol := solve({subs(eq[1 .. 5], eq[6])}, {Vi, Vo})
sol1 := eval(Vo/Vi, sol)
form := a*(s^2+b*s+c)/(s^2+d*s+e)
sol2 := solve(identity(sol1 = form, s), {a, b, c, d, e})
Vo/Vin = eval(form, sol2)

I'm looking for Vo in terms of Vi and the R, and C parameters but not Va and Vb (these are intermediate voltages).  There seems to be a solution when I work it out manually using subs and solve commands.  Any help is much appreciated.



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