Which of the following states the pythagorean theorem?

a. in a right triangle, the square of the hypotenuse equals the sum of the squares of the legs.
b. in a right triangle, the hypotenuse equals the sum of the squares of the legs.
c. in a right triangle, the hypotenuse equals the sum of the legs.
d. in a right triangle, the square of the hypotenuse equals the sum of the legs.