# Do you really need "contour" here? (2)

Calculus Level 4

$\large \int_{-\infty}^{\infty} \dfrac{\cos x}{1+x^{2}} \, dx$

Find the value of the closed form of the above integral.

Bonus:

• Solve this question without using contour integration.

• Generalise $\displaystyle \int_{-\infty}^{\infty} \dfrac{\cos(x)}{a^{2}+x^{2}} dx$, where $a$ is a constant.

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