Let's start first with why one would want to use this. Well op amps usually behave quite well in terms of distortion when the output is loadless. As soon as you load the output (especially with a low impedance load) the op amp starts straying from the ideal characteristics mentioned in the datasheet, at some point even completely failing at delivering the given specs to the load. Well a simple solution is to cancel the load. How can we do that? Well a simple resistor presents a positive AC impedance, so it stands to reason that applying the same amount of negative resistance would cancel out the impedance that the first op amp sees. Rl+(-Rl)=∞Ohm theoretically. So this is how it works. The first stage acts as a voltage amplifier as any other amplifier does. But instead of handling the current amplification too it only carries the voltage one. The current amplification is shifted to the second op amp, but not in a regular way like you'd do, but through a negative resistance feedback. Basically the second op amp has a gain of two to compensate the attenuation through the negative resistance feedback (the other 200ohm resistor). Note that the parameters of the second op amp don't influence the performance of the first one. So basically you can get a power Op Amp and a low noise op amp, and use this topology to make a power amp with the distortion specs of an unloaded low distortion small signal op amp.
