12) What is the term for the curve traced by a point moves in a plane in such a way that the sum of its distance from two fixed points is constant?

13) What is the eccentricity of parabola?

14) Which is a practical application of parabolic curve?

15) What is the circle that rolls on a straight line or on the arc of a circle to generate cycloidal curves on its circumference?

16) What is the term for the locus of a point lying on the circumference of the circle which rolls on a straight line?