Fusk musk

 A Fourier series (/ˈfʊrieɪ, -iər/^[1]) is a sum that represents a periodic function as a sum of sine and cosine waves. The frequency of each wave in the sum, or harmonic, is an integer multiple of the periodic function's fundamental frequency. Each harmonic's phase and amplitude can be determined using harmonic analysis. A Fourier series may potentially contain an infinite number of harmonics. Summing part of but not all the harmonics in a function's Fourier series produces an approximation to that function. For example, using the first few harmonics of the Fourier series for a square wave yields an approximation of a square wave.

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  A square wave (represented as the blue dot) is approximated by its sixth partial sum (represented as the purple dot), formed by summing the first six terms (represented as arrows) of the square wave's Fourier series. Each arrow starts at the vertical sum of all the arrows to its left (i.e. the previous partial sum).

 
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  The first four partial sums of the Fourier series for a square wave. As more harmonics are added, the partial sums converge to (become more and more like) the square wave.

 
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  Function ${\displaystyle s_{6}(x)}$ (in red) is a Fourier series sum of 6 harmonically related sine waves (in blue). Its Fourier transform ${\displaystyle S(f)}$ is a frequency-domain representation that reveals the amplitudes of the summed sine waves.