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."
In mathematical terms, if a right triangle has legs of lengths \(a\) and \(b\), and a hypotenuse of length \(c\), the Pythagorean theorem is expressed as \(a^2 + b^2 = c^2\).