Mathematics · Parabola

JEE Main 2026 — 5 April, Evening Shift — Question 36

Let the directrix of the parabola P:y2=8xP: y² = 8x cut x-axis at point A. Let B(α,β)α>1B(α,β) α>1 be a point on PP such that the slope of AB is 3/5.3/5. If BCBC is a focal chord of P,P, then six times the area of ΔABCΔABC is :

  1. Option A:

    8080

  2. Option B:

    160160

    Correct
  3. Option C:

    174174

  4. Option D:

    192192

Answer: B

Step-by-step solution

Given parabola: y2=8xy^2 = 8x. Directrix: x=−2x = -2, so A(−2,0)A(-2,0). Let B(2t2,4t)B(2t^2, 4t) on parabola. Slope of AB: 4t2t2+2=35\frac{4t}{2t^2+2} = \frac{3}{5}. Cross-multiply: 20t=6t2+620t = 6t^2 + 6. 3t2−10t+3=03t^2 - 10t + 3 = 0. t=3t = 3 or t=13t = \frac{1}{3}. Since α>1\alpha > 1, t=3t = 3. Thus B(18,12)B(18,12). Focal chord BC: other end C(2t2,−4t)=(29,−43)C \left( \frac{2}{t^2}, -\frac{4}{t} \right) = \left( \frac{2}{9}, -\frac{4}{3} \right). Area of △ABC\triangle ABC: 12∣−2(12+43)+18(−43−0)+29(0−12)∣\frac{1}{2} \left| -2(12 + \frac{4}{3}) + 18(-\frac{4}{3} - 0) + \frac{2}{9}(0 - 12) \right|. Simplify: 12∣−2⋅403+18⋅(−43)+29⋅(−12)∣=12∣−803−24−83∣=12⋅1603=803\frac{1}{2} \left| -2 \cdot \frac{40}{3} + 18 \cdot \left(-\frac{4}{3}\right) + \frac{2}{9} \cdot (-12) \right| = \frac{1}{2} \left| -\frac{80}{3} - 24 - \frac{8}{3} \right| = \frac{1}{2} \cdot \frac{160}{3} = \frac{80}{3}. Six times area: 6×803=1606 \times \frac{80}{3} = 160.

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Subject
Mathematics
Chapter
Parabola
Topic
Introduction to Parabola