Heron's formula is useful when we know the lengths of all three sides of a triangle and want to find its area. This formula does not require any information about the angles, making it unique for such cases.

From the options provided, the correct answer is: A. Heron’s formula is used when the three lengths of the sides of a triangle are known.

Would you like a detailed explanation of Heron's formula?

Here are some related questions that might expand your understanding:

1. How is Heron's formula derived from basic geometric principles?
2. What are the steps to calculate the semi-perimeter in Heron's formula?
3. Can Heron's formula be applied to any type of triangle, including obtuse and right triangles?
4. How does Heron's formula differ from other methods for finding a triangle's area?
5. What are some practical applications of Heron's formula in real-world problems?

Tip: Always double-check your triangle side lengths to ensure they satisfy the triangle inequality when using Heron's formula.