RC Filter Circuit Question
$$
V_o  = V_s * \frac{Z}{Z+R1}
$$
 where
$$
Z = \frac{R_2}{j\omega R_2C +1}
$$
Thus

$$ 
\frac{V_o}{V_s} = \frac{Z}{Z+R_1}
$$

$$
\frac{V_o}{V_s} = \frac{R_2}{j\omega R_1 R_2C+R_1+R_2}
$$