Explain how an ideal triangular shaped waveform can be produced from sinusoidal waveforms?

A shot in the dark here, since I'm not greatly familiar with the subject matter. Check out Fourier series as an approximation. They use the sum of a group of sinusoidal waves to form common patterns. My experience in it is with loading for structural engineering of plates, but from a math standpoint it should be similar (building a shape based on summing odd or even multiples of the waves).