JEE Main201912 Apr 2019Evening ShiftMathematicsHyperbolaActual
The equation of a common tangent to the curves, y 2 = 16 x and x y = - 4 , is:
Options
- Ax - 2 y + 16 = 0
- Bx - y + 4 = 0
- C2 x - y + 2 = 0
- Dx + y + 4 = 0
Correct answer
B. x - y + 4 = 0
Step-by-step solution
A tangent to the parabola y 2 = 16 x can be written as: y = m x + 4 m …. (1) It will touch the hyperbola x y =   – 4 ,   if the quadratic x m x + 4 m = – 4 has coincident roots, ⇒ m 2 x 2 + 4 x + 4 m = 0 ,   D ≡ 16 - 16 m 3 = 0 ⇒ m = 1 ⇒ Equating of common tangent will be y = x + 4 ⇒ x - y + 4 = 0