JEE Main 2021
Conic Sections
Parabola
Medium
Question
A line is a common tangent to the circle (x 3) 2 + y 2 = 9 and the parabola y 2 = 4x. If the two points of contact (a, b) and (c, d) are distinct and lie in the first quadrant, then 2(a + c) is equal to _________.
Answer: 3
Solution
This problem involves finding a common tangent line to a parabola and a circle, identifying their respective points of contact in the first quadrant, and then performing a specific calculation based on these coordinates. We will leverage the standard forms of tangent equations and the condition for tangency.
1. Key Concepts and Formulas
- Equation of a Tangent to a Parabola: For a parabola of the standard form , the equation of a tangent line with slope is given by: The coordinates of the point of contact for this tangent on the parabola are: