Explanation: A square wave is a classic example of a complex waveform that can be understood through Fourier analysis. According to Fourier's theorem, any periodic complex waveform can be decomposed into a sum of simple sine (or cosine) waves of different frequencies and amplitudes. For a perfect square wave, its composition consists of a fundamental sine wave (the lowest frequency component) and an infinite series of its odd harmonics (3rd, 5th, 7th, etc.), each with progressively smaller amplitudes. The specific combination of these odd harmonics creates the characteristic sharp rising and falling edges and the flat tops of the square wave. Even harmonics are absent due to the waveform's symmetry. A sine wave (and a cosine wave, which is merely a phase-shifted sine wave) represents a single, pure frequency, not a composite of multiple frequencies. A tangent function describes a mathematical relationship and is not used to describe the composition of electromagnetic waves in this context.