Explanation:
In order to find the hypotenuse of a right triangle, you must remember the theorem:
a² + b² = c².
40 to the second power is 1600, and 9 to the second power is 81.
Add these together for a total of 1681, but you're not done yet. We need to find what multiplied by itself equals 1681, since c is to the second power.
The square root is 41, so x is 41.