To find the length of the diagonal of a rectangle, we can use the Pythagorean theorem. The diagonal, along with the width and length, forms a right triangle. According to the Pythagorean theorem, the square of the hypotenuse (the diagonal, in this case) is equal to the sum of the squares of the other two sides.
The formula for the diagonal (d) is:
d = √(width² + length²)
Given that the width is 9 units and the length is 40 units, we can plug these values into the formula:
d = √(9² + 40²)
d = √(81 + 1600)
d = √(1681)
d = 41
Thus, the length of the diagonal is 41 units.