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matt grime
Mar8-04, 05:38 PM
Sci Advisor
HW Helper
P: 9,396
There is no uniform way of doing these things so I'm going to have to guess - do you mean why is there no cos(kx) involved, where k is whatever the constants work out to be?

Presumably the oscillating string has its end points fixed, so imgane extending the string into negative x - the resulting shape is an odd function - it has rotation symmetry of 180 degrees about the origin, so in its fourier expansion there will ony be odd terms and therefore no cos(kx)s involved.