A3. A square is inscribed in a circle with radius $r$. The length of the side of the square is:
(A) $2 r \sqrt{2}$
(B) $r \sqrt[3]{3}$
(C) $\frac{r}{\sqrt{2}}$
(D) $\frac{r}{2}$
(E) None of the above answers is correct.

![](https://cdn.mathpix.com/cropped/2024_06_07_bce9c6e2a6f4f88bb0deg-06.jpg?height=491&width=488&top_left_y=1499&top_left_x=1429)
A3. Let's draw a sketch. From the sketch, it is clear that the diagonal of the square $d=2r$ or $d=a\sqrt{2}$. From this, we have $2r=a\sqrt{2}$. Expressing the side length $a=r\sqrt{2}$. The correct answer is E.