Recall that $x = r\cos\theta$, $y = r\sin\theta$, and $dx\,dy = r\,dr\,d\theta$. So, we have:
$$\int\int 2x\sqrt{x^2 + y^2}\,dy\,dx = \int\int 2(r\cos\theta)r\,r\,dr\,d\theta$$
Now, we need to find the limits of integration. Since we are not given any specific
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