Answer:
a = 4 cm
Step-by-step explanation:
Using Pythagoras' identity in the right triangle.
The square on the hypotenuse is equal to the sum of the squares on the other 2 sides, that is
a² + 3² = 5²
a² + 9 = 25 ( subtract 9 from both sides )
a² = 16 ( take the square root of both sides )
a = = 4