Resembling resemblance?

Calculus Level 4

Let F ( n ) = 0 sin ( x n ) x d x . F(n)=\int^{\infty}_0\frac{\sin(x^n)}{x} \, dx. Then find lim n F ( n ) . \lim\limits_{n\to\infty}F(n).


The answer is 0.

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1 solution

Aditya Agarwal
Jan 5, 2016

The given integral can be computed as follows: 0 sin ( x n ) x d x = 1 n 0 ( n x n 1 ) sin ( x n ) x n d x \int^{\infty}_0\frac{\sin(x^n)}{x}dx=\frac1n\int^{\infty}_0\frac{(nx^{n-1})\sin(x^n)}{x^n}dx With an appropriate substitution, the given integral becomes the well known Dirichlet Integral. So the limit lim n π 2 n = 0 \lim\limits_{n\to\infty}\frac{\pi}{2n}=0

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