Let P be a point on the parabola y 2 = 4 a x , where a > 0 . The normal to the parabola at P meets the x…

Let P be a point on the parabola y2=4ax, where a>0. The normal to the parabola at P meets the x-axis at a point Q. The area of the triangle PFQ, where F is the focus of the parabola, is 120. If the slope m of the normal and a are both positive integers, then the pair a, m is
  1. 2, 3
  2. 1, 3
  3. 2, 4
  4. 3, 4

Solution

Given,

Parabola y2=4ax,

Now plotting the normal to parabola at point Pam2,-2am, we get

So, equation of normal at Pam2, -2am is y=mx-2am-am3

Hence, point Q2a+am2,0

And focus of parabola will be Fa,0

Now finding the area of PFQ we get,

Area of PFQ=12a+am2×2am=120

a2m1+m2=120

So, possible pair from option will be,

a, m2, 3 which satisfies above equation

Asked in: JEE Advanced 2023 (Paper 1)

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