The general equation for an AC sinusoidal voltage is
where is the amplitude of the voltage waveform, the highest voltage this wave attains.

The average value is a pretty common and useful concept, yet its meaning is often misunderstood.
The average value of a sine waveform over a full cycle is zero. For symmetrical waveforms such as the sine, the average value is calculatedover a half cycle rather than the full cycle.

This brings us to