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In this video, we're going to go through the answer to question number 16 from chapter 10 .3.
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So it has to find the fourier series of function f, which is piecewise defined.
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So it's zero from minus pi to minus pi by two.
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It's minus one from minus pi by two to zero.
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It's one from zero to pi by two, and it's zero from pi by two to pi.
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So it kind of starts off as zero, then it goes to minus one, and it goes to plus one.
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And it goes to zero again.
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So we need to sort of fit a fourier series to this.
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So we need to find the a -ns and b -ns.
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So first the a -ns.
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So this is the one over pi, because l is pi in this case.
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So we don't need to integrate when it's zero, or rather for these values, the integral is just going to be zero, so we can just forget about that.
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So we only need to integrate between minus pi in pi by 2.
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So we'll introduce this function, the sign function or the signum function.
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So all this is is a function that is, it just gives the sign of x.
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So in x is negative, it will give minus 1...