RLC circuit magnitude of the transfer function
Apply the voltage divider: \$\frac{V_R}{V_S}=\frac{R}{R+j\omega L-\frac{j}{\omega C}}=\frac{\omega CR}{\omega CR+j\omega^2CL-j}=\frac{\omega CR}{\omega CR+j(\omega^2CL-1)}\$

Then take the magnitude.