2nd order passive RC filter Transer Function

Hi I need to derive the Transfer Function for the circuit i have attached. I am just not able to get there. I am almost there, but i think I have done something wrong and I just cannot find what is wrong.
Can some1 pls show me the full working. I have done it with help of Thevenin Equivalents. But as i said cannot get the correct function.
pls help me

btw: tau1=R1*C1 tau2=R2*C2 tau12=R1*C2 and assume that R1=R3

 

It would be good if you can post your solution. That way we can assist you in identifying where you took a wrong turn in your effort.

hgmjr

 

After working through the calculations, I was able to duplicate the answer contained in your attachment with one exception. The answer I arrived at does not contain the quantity -1 in the denominator. In my answer, the corresponding value is +1. In all other respects, the answer I have calculated matches the one given in the attachment term for term.

I hope you will be able to post your work soon so that we can try to spot where you may be having a problem with your calculation.

hgmjr