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JEE Main 20238 AprilEvening Shift
Exam
JEE Main
Year
2023
Date
8 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Straight Lines

JEE Main 2023 · 8 April · Evening Shift · Mathematics · Straight Lines

Let A ( 0, 1 ) , B ( 1, 1 ) and C ( 1, 0 ) be the mid-points of the...

Let A(0,1),B(1,1)A ( 0, 1 ) , B ( 1, 1 ) and C(1,0)C ( 1, 0 ) be the mid-points of the sides of a triangle with incentre at the point DD. If the focus of the parabola y2=4ax{y}^{2} = 4ax passing through DD is (α+β2,0)( \alpha + \beta\sqrt{2}, 0 ), where α\alpha and β\beta are rational numbers, then αβ2\dfrac{\alpha}{{\beta}^{2}} is equal toLet A ( 0, 1 ) , B ( 1, 1 ) and C ( 1, 0 ) be the mid-points of the sides of a triangle with incentre at the point D .

Options

  1. A88
  2. B1212
  3. C66
  4. D92\dfrac{9}{2}

Correct answer

A. 88

Step-by-step solution

Given,

A(0,1),B(1,1)A ( 0, 1 ) , B ( 1, 1 ) and C(1,0)C ( 1, 0 ) be the mid-points of the sides of a triangle with incentre at the point DD,

Now finding the vertices of the triangle by using midpoint formula and plotting the diagram we get,

Let A ( 0, 1 ) , B ( 1, 1 ) and C ( 1, 0 ) be the mid-points of the sides of a triangle with incentre at the point D .

Now finding the incentre of the above triangle using the formula,

I≡(ax1+bx2+cx3a+b+c,ay1+by2+cy3a+b+c)I ≡ \left(\dfrac{a{x}_{1} + b{x}_{2} + c{x}_{3}}{a + b + c}, \dfrac{a{y}_{1} + b{y}_{2} + c{y}_{3}}{a + b + c}\right)

We get, Incentre D=(44+22,44+22)D = \left(\dfrac{4}{4 + 2\sqrt{2}}, \dfrac{4}{4 + 2\sqrt{2}}\right)

Now given parabola y2=4ax{y}^{2} = 4ax passes through the incentre DD we get,

(44+22)2=4a(44+22){\left(\dfrac{4}{4 + 2\sqrt{2}}\right)}^{2} = 4a\left(\dfrac{4}{4 + 2\sqrt{2}}\right)

⇒a=14+22⇒ a = \dfrac{1}{4 + 2\sqrt{2}}

Now we know that focus of parabola is given by, focus (a,0)( a, 0 )

Hence, focus will be,\left(\dfrac{1}{4 + 2\sqrt{2}}, 0\right) = \left(\dfrac{4 - 2\sqrt{2}}{8}, 0\right)</p><p><br/>Nowcomparingwith</p><p><br />Now comparing with( \alpha + \beta\sqrt{2}, 0 )weget,</p><p>we get,</p><p>\alpha = \dfrac{4}{8} = \dfrac{1}{2}, \beta = - \dfrac{1}{4}<br/>Hence,<br />Hence,\dfrac{\alpha}{{\beta}^{2}} = \dfrac{\dfrac{1}{2}}{{\left(\dfrac{- 1}{4}\right)}^{2}} = \dfrac{16}{2} = 8

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