A circle with centre O and radius 4 cm is inscribed in a rectangle ABCD. What is the length of the diagonal of the rectangle?
Correct: C
Since the circle with radius 4 cm is inscribed in the rectangle, the diameter of the circle is 8 cm. So the length of the side of the rectangle is 8 cm. Let the length of the other side be x. Then, the diagonal is √(8^2 + x^2). We also know that the diameter of the circle is the width of the rectangle. So, the width of the rectangle is also 8 cm. Therefore, x = 8. Hence, the length of the diagonal = √(8^2 + 8^2) = √128 = 8√2.