The correct statement that explains the Pythagorean Theorem is:
If a triangle is a right triangle, then the sum of the squares of the legs is equal to the square of the hypotenuse.
This means that if a triangle has a right angle, the relationship between the lengths of the two legs (the sides adjacent to the right angle) and the hypotenuse (the side opposite the right angle) can be expressed mathematically as \( a^2 + b^2 = c^2 \), where \( c \) is the hypotenuse.