NTA Abhyas JEE Main2020MathematicsParabolaPractice
If three normals are drawn from the point c , 0 to the parabola y 2 = 4 x and two of which are perpendicular, then the value of c is equal to
Options
- A3
- B4
- C5
- D6
Correct answer
A. 3
Step-by-step solution
Equation of the normal in slope form is y = m x - 2 m - m 3 which passes through c , 0 ⇒ 0 = m c - 2 m - m 3 ⇒ m 3 + 2 - c m = 0 ⇒ m = 0 or m 2 + 2 - c = 0 ⇒ m 1 m 2 = 2 - c 1 = - 1 ⇒ c = 3