If one end of a focal chord of the parabola y² = 16x is at (1, 4), then the length of this focal chord is?

The correct option is A
25
y² = 4ax = 16x ⇒ a = 4
A(1, 4) ⇒ 2.4.t₁ = 4 ⇒ t₁ = 1/2
∴ length of focal chord = a(t + 1/t)² = 4(1/2 + 2)² = 4 × 25/4 = 25.