Engineering
Mathematics
Tangent of Parabola
Question

If one end of a focal chord AB of the parabola y2 = 8x is at A(12,−2), then the equation of the tangent to it at B is :

2x - y - 24 = 0

2x + y - 24 = 0

x - 2y + 8 = 0

x + 2y + 8 = 0

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Solution

Let   (12,−2)  is  (2t2,4t)⇒t=−12

Parameter of other end of focal chord is 2

⇒ point is (8, 8)

⇒ equation of tangent is 8y – 4(x+8) = 0

⇒ 2y – x = 8