Evaluate power and efficiency in opamp, exercise
The dc current drawn from the 15-V supply is 8 mA.

Calculate total power into circuit like this: power = Vdc * Idc = 0.12 watts.

...provides a 12-V peak-to-peak sine-wave signal to a 1- kΩ load

The RMS voltage is 4.243 volts (figure that out) hence the power in the load is 18 mW (again you should figure that out yourself).
The Power dissipated in the amplifier is the difference i.e. 0.102 W
The efficiency is power out / power in * 100% = 15%.
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