Answer
(a) $606~\Omega$
(b) increase
Work Step by Step
(a) We can find the impedance as:
$cos \phi=\frac{R}{Z}$
This can be rearranged as:
$Z=\frac{R}{cos\phi}$
We plug in the known values to obtain:
$Z=\frac{525}{cos30^{\circ}}$
$Z=606~\Omega$
(b) We know that $(X_L-X_C)^2=(\omega L-\frac{1}{\omega}C)^2$. This equation shows us that when frequency is increased then $(X_L-X_C)^2$ is also increased. As a result, impedance will increase because impedance depends on $(X_L-X_C)^2$; that is, $Z=\sqrt{R^2+(X_L-X_C)^2}.$
