The Pythagorean theorem states that for any right triangle, the square of the hypotenuse is equal to the sum of the squares of the two legs. The distance formula calculates the distance between two points (x1, y1) and (x2, y2) by taking the square root of the sum of the squares of the differences between the x- and y-coordinates. The document provides an example of using each formula to calculate the length of a side of a triangle and the distance between two points.