Electrical AC circuit is built with two resistors, capacitor and inductivity. Impedances of all elements are known. Parts in circuit are connected in series and parallel. Current I flows through circuit. Current has starting phase ψi=π/4. Ohm's law for AC circuit is applied to designate circuit's supply voltage U → U=Z·I. Circuit's total impedance Z has to be designated before applying Ohm's law. Subject of example is calculation of apparent power S, active power (real power) P and reactive power Q. Power triangle is plotted in example.