A potential followup is why we don't have a component corresponding to the -180° direction in the two-dimensional R-X plot.
Fundamentally, that would mean negative resistance: a current that flows in the direction opposite to the applied voltage, proportionally to the applied voltage. That would require the addition of energy to the system, so it's not something that can be done with a passive component. The idea can be realized with an active, powered circuit, although it's not hugely useful to do so.
A "lite" version of this idea is a device where the resistance stays positive, but drops in response to the applied voltage (at least within *some* range of voltages). This is the behavior of diodes, fluorescent lamps, and so on. But these devices are nonlinear and don't obey Ohm's law, so it's not particularly meaningful to position them as "anti-resistors".
A potential followup is why we don't have a component corresponding to the -180° direction in the two-dimensional R-X plot.
Fundamentally, that would mean negative resistance: a current that flows in the direction opposite to the applied voltage, proportionally to the applied voltage. That would require the addition of energy to the system, so it's not something that can be done with a passive component. The idea can be realized with an active, powered circuit, although it's not hugely useful to do so.
A "lite" version of this idea is a device where the resistance stays positive, but drops in response to the applied voltage (at least within *some* range of voltages). This is the behavior of diodes, fluorescent lamps, and so on. But these devices are nonlinear and don't obey Ohm's law, so it's not particularly meaningful to position them as "anti-resistors".