This circuit takes an input and provides two outputs equal to the input, but with opposite phases.
The capacitor and the 150k and 56k resistors bias the transistor. The base-emitter junction acts like a diode, so that the emitter will be a diode drop lower than the base.
The emitter voltage fluctuates with the input voltage, and so the current across the emitter resistor fluctuates proportionately. Since the collector resistor has the same current across it, the collector voltage swings the same amount, but with phase opposite to the input, because the larger the current, the larger the voltage drop from +20V.
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