The transfer function for a 2nd order opamp low pass filter
You can apply the fast analytical circuit techniques or FACTs to determine this transfer function almost by inspection. This is actually an example of the book I wrote on the subject. The principle lies in finding the time constants involving each of the energy-storing elements, the two capacitors in your circuit. First, you start for \$s=0\$ and open the caps. You have a simple voltage follower whose gain is 1:

Then, determine the resistance \$R\$ driving each capacitor to determine the time constant \$\tau=RC\$ when the stimulus source is zeroed (\$V_{in}\$ is replaced by a short circuit). You determine a resistance across terminals by installing a test generator \$I_T\$ which develops a voltage \$V_T\$: the resistance you want is simply: \$R=\frac{V_T}{I_T}\$. Here we go for \$\tau_1\$ and \$\tau_2\$:

In the left side, you see that the current source generates a voltage \$V_1\$ which biases the (+) pin and is thus duplicated on the output and the (-) input: there is 0 V across the current source (considering an infinite open-loop gain for the op-amp) and thus \$\tau_1 = 0\cdot C_1=0\;\mathrm s\$ and since the current source in the right-side drawing only biases the resistances in series, you have: \$\tau_2=(R_1+R_2)C_2\$. We can already form the first-order coefficient of our denominator: \$b_1=(R_1+R_2)C_2\$.
For the second-order time constant, we set \$C_2\$ in its high-frequency state and determine the resistance offered by \$C_1\$'s terminals.

In this mode, because the voltage at the (+) pin is 0 V, so is the right-side of the current source. Therefore, the voltage \$V_T\$ depends on the two paralleled resistors: \$\tau_{21}=C_1(R_1||R_2)\$. And that's it! We have our denominator formed as: \$D(s)=1+sb_1+s^2b_2=1+s(\tau_1+\tau_2)+s^2(\tau_2\tau_{21})=1+\frac{s}{Q\omega_0}+(\frac{s}{\omega_0})^2\$. There are no zeroes in this transfer function and a quick Mathcad sheet plots the response for you:

The FACTs get you straight to the answer by inspection, without writing a single line of algebra. Furthermore, the transfer function is directly expressed in a low-entropy form where meaningful parameters such as a quality factor and a resonant frequency show up naturally.