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Let PQ be a focal chord of the parabola ...

Let PQ be a focal chord of the parabola `y^2 = 4ax` The tangents to the parabola at P and Q meet at a point lying on the line `y = 2x + a, a > 0`. Length of chord PQ is

A

7a

B

5a

C

2a

D

3a

Text Solution

Verified by Experts

The correct Answer is:
B
Since, `R [-a,a (r - (1)/(t))]` lies on `y = 2x + a`.

`implies a (t - (1)/(t)) = - 2a + a implies t - (1)/(t) = - 1`
Thus, length of focal chord
`= a (t + (1)/(t))^(2) = a {(t - (1)/(t))^(2) + } = 5a`
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