Ariel's work is not correct because she did not identify the longest side correctly when applying the Pythagorean theorem. For a triangle to be a right triangle, the square of the length of the longest side must equal the sum of the squares of the lengths of the other two sides.
In this case, the side lengths are 9, 12, and 15, and the longest side is 15, not 12. Therefore, the correct application of the Pythagorean theorem should be:
\( 9^2 + 12^2 = 15^2 \)
Calculating these values gives:
\( 9^2 = 81 \)
\( 12^2 = 144 \)
\( 15^2 = 225 \)
Now, we check if the equation holds:
\( 81 + 144 = 225 \)
Since both sides are equal, we see that the triangle with side lengths 9, 12, and 15 actually forms a right triangle. Thus, Ariel's conclusion that these lengths do not form a right triangle is incorrect.