If a rectangle is inscribed in a circle, the diagonal of the rectangle is equal to the diameter of the circle. This is because the diagonal spans across the entire circle, touching both sides of the circle.

Given:

• Radius of the circle = 15 cm

The diameter of the circle is twice the radius: $\text{Diameter} = 2 \times \text{Radius} = 2 \times 15 = 30 \text{ cm}$

Thus, the length of the diagonal of the rectangle is 30 cm.

Would you like to explore further details or ask any related questions? Here are 5 questions that might interest you:

1. How do you find the area of a rectangle inscribed in a circle?
2. Can the area of the circle be related to the dimensions of the rectangle?
3. What are the possible side lengths of the rectangle?
4. How does the Pythagorean theorem apply to the rectangle's diagonal?
5. Can this be extended to three dimensions (e.g., a rectangular box inside a sphere)?

Tip: The relationship between a rectangle inscribed in a circle and the circle's properties often involves both geometry and trigonometry.