What angle is the voltage or current is momentarily constant?

In an alternating current (AC) circuit, the voltage or current is momentarily constant at the peak of its sinusoidal waveform. This occurs when the waveform reaches its maximum or minimum value, resulting in a momentary pause where the rate of change is zero. At these points, the angle of the waveform corresponds to 90 degrees (π/2 radians) or 270 degrees (3π/2 radians), depending on whether it is at the positive or negative peak, respectively.