Question

The common tangent of the parabolas y² = 4x and x² = –8y is–

• A. y = x + 2
• B. y = x – 2
• C. y = 2x + 3
• D. None

Answer 1

Answer: (D)

None

Answer 2

y² = 4x ...(1)

̃ 4a = 4 ̃ a = 1

equation of tangent of parabola (1) is

y = mx + a/m ̃ y = mx + 1/m ...(2)

Q Another parabola is x² = – 8y ...(3)

Now, line (2) touches the parabola (3) then the equation

x² = –8$\left( mx + \frac{1}{m} \right)$ has equal roots

̃ Discriminant = 0 ̃ m = ?

put in 2