Let be the exponential:(adsbygoogle = window.adsbygoogle || []).push({});

[tex] e^{inx}=cos(nx)+isin(nx) [/tex] [tex] n\rightarrow \infty [/tex]

Using the definition (approximate ) for the delta function when n-->oo

[tex] \delta (x) \sim \frac{sin(nx)}{\pi x} [/tex] then differentiating..

[tex] \delta ' (x) \sim \frac{ncos(nx)}{\pi x}- \frac{\delta (x)}{\pi x} [/tex]

are this approximations true for big "n" ??.. i would like to know this to compute integrals (for big n ) of the form:

[tex] \int_{2}^{\infty} dx f(x,n)e^{inx} [/tex]

thanks.... :grumpy: :tongue2:

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# Dirac delta and exponential

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