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JEE Advanced 2023Paper 1
Exam
JEE Advanced
Year
2023
Paper
Paper 1
Subject
Mathematics
Chapter
Parabola

JEE Advanced 2023 · Paper 1 · Mathematics · Parabola

Let P be a point on the parabola y ^ 2 = 4ax , where a > 0 . The...

Let PP be a point on the parabola y2=4ax{y}^{2} = 4ax, where a>0a > 0. The normal to the parabola at PP meets the xx-axis at a point QQ. The area of the triangle PFQPFQ, where FF is the focus of the parabola, is 120120. If the slope mm of the normal and aa are both positive integers, then the pair (a,m)\left(a, m\right) isLet P be a point on the parabola y ^ 2 = 4ax , where a > 0 . The normal to the parabola at P meets the x -axis at a

Options

  1. A(2,3)\left(2, 3\right)
  2. B(1,3)\left(1, 3\right)
  3. C(2,4)\left(2, 4\right)
  4. D(3,4)\left(3, 4\right)

Correct answer

A. (2,3)\left(2, 3\right)

Step-by-step solution

Given,

Parabola y2=4ax{y}^{2} = 4ax,

Now plotting the normal to parabola at point P(am2,−2am),weget</p><p><imgsrc="https://cdn−question−pool.getmarks.app/pyq/jeeadvanced/a716b152−dac5−4209−b751−0649f2b39468.png"style="width:400px;height:219px;"/></p><p>So,equationofnormalatP\left(a{m}^{2}, - 2am\right), we get</p><p><img src="https://cdn-question-pool.Quantrex.app/pyq/jee_advanced/a716b152-dac5-4209-b751-0649f2b39468.png" style="width: 400px; height: 219px;" /></p><p>So, equation of normal atP\left(a{m}^{2}, - 2am\right)isisy = mx - 2am - a{m}^{3}</p><p>Hence,point</p><p>Hence, pointQ\left(2a + a{m}^{2}, 0\right)

And focusofparabolawillbeF(a,0)of parabola will beF\left(a, 0\right)

Now finding the area of ∆PFQ∆ PFQ we get,

Area of ∆PFQ=12(a+am2)×2am=120∆ PFQ = \dfrac{1}{2}\left(a + a{m}^{2}\right) \times 2am = 120

⇒a2m(1+m2)=120⇒ {a}^{2}m\left(1 + {m}^{2}\right) = 120

So, possible pair from option will be,

\left(a, m\right) ≡ \left(2, 3\right) which satisfies above equation

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