This is a Class B amplifier, or push-pull follower. There is no voltage gain, but it amplifies current 100x. It's more efficient than a simple class A, which is always conducting, even when there is no input at all. This dissipates a lot of power. The push-pull only draws current proportional to the output.
One drawback of the push-pull is crossover distortion. The output is distorted whenever it crosses ground. We can improve on this.
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