Let's find the length of the side of the pool.
Let it be x, so the diagram is:
Using the pythagorean theorem, we can figure out x. Shown below:
![\begin{gathered} x^2+40^2=50^2 \\ x^2=50^2-40^2 \\ x^2=900 \\ x=\sqrt[]{900} \\ x=30 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/kdp669vjlepwy9aangcttzg54dnl53bu1b.png)
So, 30 meters is the side length of the square (pool).
The area of a square is:

Where "s" is the side length
We found s to be 30, thus the area of the pool is:

Thus,
Ulysses is correct.