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JEE Main 20203 SeptemberMorning Shift
Exam
JEE Main
Year
2020
Date
3 September
Shift
Morning Shift
Subject
Mathematics
Chapter
Quadratic Equation

JEE Main 2020 · 3 September · Morning Shift · Mathematics · Quadratic Equation

If α and β are the roots of the equation x ^ 2 + px + 2 = 0 and...

If α\alpha and β\beta are the roots of the equation x2+px+2=0{x}^{2} + px + 2 = 0 and 1α\dfrac{1}{\alpha} and 1β\dfrac{1}{\beta} are the roots of the equation 2x2+2qx+1=0,2{x}^{2} + 2qx + 1 = 0, then \left(\alpha - \dfrac{1}{\alpha}\right)(β−1β)(α+1β)(β+1α)\left(\beta - \dfrac{1}{\beta}\right)\left(\alpha + \dfrac{1}{\beta}\right)\left(\beta + \dfrac{1}{\alpha}\right) is equal to :

Options

  1. A94(9+q2)\dfrac{9}{4}\left(9 + {q}^{2}\right)
  2. B94(9−q2)\dfrac{9}{4}\left(9 - {q}^{2}\right)
  3. C94(9+p2)\dfrac{9}{4}\left(9 + {p}^{2}\right)
  4. D94(9−p2)\dfrac{9}{4}\left(9 - {p}^{2}\right)

Correct answer

D. 94(9−p2)\dfrac{9}{4}\left(9 - {p}^{2}\right)

Step-by-step solution

α,β\alpha, \beta are roots of x2+px+2=0{x}^{2} + px + 2 = 0

⇒α+β=−p,αβ=2⇒ \alpha + \beta = - p, \alpha\beta = 2

1α,1β\dfrac{1}{\alpha}, \dfrac{1}{\beta} are roots of 2x2+2qx+1=02{x}^{2} + 2qx + 1 = 0

∴α,β∴ \alpha, \beta are roots of x2+2qx+2=0{x}^{2} + 2qx + 2 = 0

⇒α+β=−2q,αβ=2⇒ \alpha + \beta = - 2q, \alpha\beta = 2

∴p=2q...(i)∴ p = 2q . . . ( i )

⇒(α−1α)(β−1β)(α+1β)(β+1α)={αβ−αβ−βα+1αβ}⋅{αβ+1αβ+2}⇒ \left(\alpha - \dfrac{1}{\alpha}\right)\left(\beta - \dfrac{1}{\beta}\right)\left(\alpha + \dfrac{1}{\beta}\right)\left(\beta + \dfrac{1}{\alpha}\right) = \left\{\alpha\beta - \dfrac{\alpha}{\beta} - \dfrac{\beta}{\alpha} + \dfrac{1}{\alpha\beta}\right\} \cdot \left\{\alpha\beta + \dfrac{1}{\alpha\beta} + 2\right\}

⇒{2−((α+β)2−2αβαβ)+12}⋅⇒ \left\{2 - \left(\dfrac{{\left(\alpha + \beta\right)}^{2} - 2\alpha\beta}{\alpha\beta}\right) + \dfrac{1}{2}\right\} \cdot\left\{2 + \dfrac{1}{2} + 2\right\}</p><p></p><p>⇒ {52−(p2−42)}⋅{92}=94(9−p2)\left\{\dfrac{5}{2} - \left(\dfrac{{p}^{2} - 4}{2}\right)\right\} \cdot \left\{\dfrac{9}{2}\right\} = \dfrac{9}{4}\left(9 - {p}^{2}\right) or, 94(9−4q2)\dfrac{9}{4}\left(9 - 4{q}^{2}\right)

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