Yes, an AC (alternating current) signal can be represented as a sum of square or triangle waves using Fourier series. The Fourier series is a mathematical tool that allows us to decompose a periodic function into a sum of sinusoidal components.
A square wave can be represented as a sum of odd harmonics of the fundamental frequency. The fundamental frequency corresponds to the frequency of the AC signal, and the odd harmonics are integer multiples of the fundamental frequency (3rd harmonic, 5th harmonic, 7th harmonic, and so on). Each harmonic is a sinusoidal waveform with an amplitude and phase determined by the coefficients of the Fourier series.
A triangle wave can also be represented as a sum of odd harmonics, but with different amplitudes and phase relationships compared to the square wave. The coefficients of the Fourier series for a triangle wave produce sinusoidal components that decrease in amplitude with increasing frequency.
By adjusting the coefficients and adding up the appropriate harmonics, it is possible to approximate an AC signal using a sum of square or triangle waves. However, it's important to note that the accuracy of the approximation depends on the number of harmonics included in the series. Using a larger number of harmonics can provide a more accurate representation of the original AC signal.