mathURL
http://mathurl.com/yal9qhwk
<img src="http://mathurl.com/yal9qhwk.png" />
![\small
u_3 = \dfrac
{1 +
s \, \left[ \, C_1 \left( R_1 + R_2 \right) + C_2 \, R_2 \, \right] +
s^2 \, C_1 \, C_2 \, R_1 \, R_2}
{s^2 \, C_1 \, C_2 \, R_1 \, R_2}
\ u_1](http://mathurl.com/yal9qhwk.png)