Answer:
The correct answer is Distance Formula
Explanation:
The shape of the conics in the conic section is characterized by a factor called eccentricity of the conic and further derivations are done using this factor.
And the eccentricity of the conics can be calculated by taking the center-to-focus distance and dividing it by the semi-major axis distance. So, to find the eccentricity of the conic, one must know how to apply the distance formula.
Hence, Distance Formula is the key to deriving the equations for conic sections