A voltage source has inner impedance of Z=Ri+jXi. To it is connected a load with impedance Z=R+jX. What value should the impedance of the load have if: a) The voltage across the load is 90 degrees out of phase with the current? b) The voltage across the load is in phase with the current? c) The current is in phase with the open circuit voltage source? Can someone give me some leads how to calculate this.