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$limlimits_{Rto0^+}intlimits_{x^2+y^2le R^2}e^{-x^2}cos(y)dxdy=?$

Mathematics Asked on December 8, 2021

$$limlimits_{Rto0^+}intlimits_{x^2+y^2le R^2}e^{-x^2}cos(y)dxdy=?$$

First I want to show $f(x,y)=e^{-x^2}cos(y)$ doesn’t go crazy at $(0,0)$ otherwise it is already clearly continuous and bounded.

So $$|e^{-x^2}cos(y)|le e^{-x^2}to 1$$ when $$x^2+y^2to 0$$

So Now finite and bounded integrand’s integral has to go 0 because region vanishes, but how to properly show it?

One Answer

The function $|e^{-x^2}cos(y)|$ is bounded by $1$ from above for any $x$ and $y$. So the absolute value of your integral is less than or equal to the area of the circle $x^2+y^2leq R^2$ times $1$.

Answered by user622002 on December 8, 2021

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