To use the Pythagorean theorem:
 ⇒ define Pythagorean theorem
- Definition of Pythagorean Theorem: the square of the length of the hypotenuse of a right triangle equals the sum of the squares of the lengths of the other two sides
 
 (look at the diagram attached for a better understanding)
Information Given:
- length of the two legs: 5, 9
 
Information Wanted:
Solve:
 

Rounded to nearest tenth:
 Answer: Length of hypotenuse is 10.3
Hope that helps!