A rectangle has a width of 9 units and a length of 40 units. What is the length of a diagonal?

A rectangle’s diagonal is the hypotenuse of a right triangle with legs equal to its width and length. Using the Pythagorean theorem, the diagonal is √(9² + 40²) = √(81 + 1600) = √1681 = 41 units. The correct choice is A, 41 units.

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