To determine what needs to be corrected in Rosanna's calculation, we can consider the context of how she arrived at the length of 225 in. If she is working with a right triangle and applying the Pythagorean Theorem, the correct formula is:
\[ c^2 = a^2 + b^2 \]
where \(c\) is the length of the hypotenuse, and \(a\) and \(b\) are the lengths of the other two legs.
- If Rosanna mistakenly added the squared hypotenuse with the square of the longest leg instead of adding both legs, her calculation would be incorrect.
- If she applied the Pythagorean Theorem correctly, then her answer would be right.
- If she arrived at the length of 225 inches by summing the squares of the legs without taking the square root, then she did not follow the Pythagorean Theorem correctly, which requires taking the square root of the sum.
- The idea of dividing the answer by 2 does not apply in the context of the Pythagorean Theorem.
Based on these considerations, the most appropriate correction would be:
Rosanna should take the square root of the sum when using the Pythagorean Theorem.
This option correctly identifies a common error in using the theorem.