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 and its length and width form a right triangle, so use the Pythagorean theorem: diagonal² = 40² + 9² = 1,600 + 81 = 1,681. Since √1,681 = 41, the diagonal is 41 units. The correct choice is C, 41 units.

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