Area of rectangle with diagonal of 5 in but length not given

Draw a rectangle with diagonal 5 in. Inside this rect. are 2 acute triangles of hypotenuse 5. Note that 3^2 + 4^2 = 5^2; thus the width of the rect. is 3 and the length is 4, with the result that the hypo. is sqrt (3^2+4^2), as expected.