Calculating voltage in RLC circuit
Because \$Z_{1} &lt;&lt; Z_{2}\$, so \$Z = Z_{1}+Z_{2} \approx Z_{2}\$.

At such a low frequency (approximately 1 Hz), \$Z_{L}\$ is very small and \$Z_{C}\$ is very large.

$$ |Z_{1}| = R_{1}||wL = 20 || 5^{-6} \approx 5^-6 \Omega$$
$$|Z_{2}| = R_{2}||1/wC = 30 ||(10^{6}/5) \approx 30 \Omega$$

And \$5^{-6} + 30  \approx 30 \$.
So \$Z \approx Z_{2}\$.

Note that at this low frequency, L is shorting out R1, and C is basically doing nothing.  However, their roles will start reversing when the frequency rises to about 2 MHz.