JEE Main 2024
Conic Sections
Parabola
Hard
Question
The sum of diameters of the circles that touch (i) the parabola at the point and (ii) the -axis, is equal to ______________.
Answer: 8
Solution
This problem combines concepts from conic sections (parabolas and their tangents) and circles (family of circles, conditions for tangency to axes, and radius calculation). We need to find circles that satisfy two distinct tangency conditions and then sum their diameters.
1. Key Concepts and Strategy
The core idea revolves around two main concepts:
- Tangent to a Parabola: Finding the slope of the tangent at a given point on the parabola using differentiation.
- Family of Circles:
- The general equation of a family of circles touching a line at a specific point is given by $$(x-x_1)^2 + (y-y_1)^2 +