See picture above. Because the circuit is semi-infinite, total impedance of circuit in the box is the same with total impedance of the whole circuit. So we can draw the circuit like picture below.
To make it easier, we should work with complex number.
Hence, the impedance of resistor, inductor, and capacitor are respectively
So the total impedance of the circuit is
And now we need to change the form, so we assume that
Then give the power of two for each sides of the equation.
And now we can get
Solving these equation, and we get
So the total impedance is
Because the real part of impedance cannot be negative, so the total impedance is
So, the magnitude of total impedance is
That's my solution.
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