Answer:
a = 5
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 + 12² = 13²
a² + 144 = 169 ( subtract 144 from both sides )
a² = 25 ( take square root of both sides )
a =
= 5