JEE Main 2020 — Parabola Question with Solution
From: JEE Main 2020 (Online) 7th January Morning Slot
Question
If y = mx + 4 is a tangent to both the parabolas, y2 = 4x and x2 = 2by, then b is equal to :
Choose an option
Show full solutionCorrect option: A
Correct answer
A-128
Step-by-step explanation
Given y = mx + 4 is tangent to both the parabolas.
Applying condition of tangent for y2 = 4x, we get
= 4
m =
For x2 = 2by line y = + 4 is tangent
x2 = 2b
x2 - - 8b = 0
For tangent to the parabola Discriminant = 0
+ 32b = 0
b = -128
Applying condition of tangent for y2 = 4x, we get
= 4
m =
For x2 = 2by line y = + 4 is tangent
x2 = 2b
x2 - - 8b = 0
For tangent to the parabola Discriminant = 0
+ 32b = 0
b = -128
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