REACTANCE IN GENERAL

Now you should get a better idea of why capacitive reactance X_C is considered negative. In a sense, it is an extension of inductive reactance X_L into the realm of negatives, in a way that generally cannot occur with resistance. Capacitors act like “negative inductors.” Interesting things happen when capacitors and inductors are combined.
Reactance can vary from extremely large negative values, through zero, to extremely large positive values. Engineers and physicists always quantify reactances as imaginary numbers. In the mathematical model of impedance, capacitances and inductances manifest themselves perpendicularly to resistance. Thus ac reactance occupies a different and independent dimension from dc resistance. The general symbol for reactance is X; this encompasses both inductive reactance X_L and capacitive reactance X_C.