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JEE Main 20204 SeptemberMorning Shift
Exam
JEE Main
Year
2020
Date
4 September
Shift
Morning Shift
Subject
Mathematics
Chapter
Quadratic Equation

JEE Main 2020 · 4 September · Morning Shift · Mathematics · Quadratic Equation

Let α and β be the roots of x ^ 2 - 3x + p = 0 and γ and be the...

Let α\alpha and β\beta be the roots of x2−3x+p=0{x}^{2} - 3x + p = 0 and γ\gamma and δ\delta be the roots of x2−6x+q=0.{x}^{2} - 6x + q = 0 . If α,β,γ,δ\alpha, \beta, \gamma, \delta from a geometric progression. Then ratio (2q+p):(2q−p)( 2q + p ) : ( 2q - p ) is

Options

  1. A3:13: 1
  2. B9:79: 7
  3. C5:35: 3
  4. D33:3133: 31

Correct answer

B. 9:79: 7

Step-by-step solution

Let α=a,β=ar,γ=ar2,δ=ar3\alpha = a, \beta = ar, \gamma = a{r}^{2}, \delta = a{r}^{3}

α+β=3⇒a+ar=3\alpha + \beta = 3 ⇒ a + ar = 3 ...........\left(1\right)</p><p></p><p>\gamma + \delta = 6 ⇒ a{r}^{2} + a{r}^{3} = 6.........(2).........\left(2\right)

By \left(1\right)and(2)⇒ar2(1+r)a(1+r)=63and \left(2\right) ⇒ \dfrac{a{r}^{2}\left(1 + r\right)}{a\left(1 + r\right)} = \dfrac{6}{3}

⇒r2=2⇒ {r}^{2} = 2

∴2q+p2q−p=2γδ+αβ2γδ−αβ=2a2r5+a2r2a2r5−a2r=2r4+12r4−1=8+18−1=97∴ \dfrac{2q + p}{2q - p} = \dfrac{2\gamma\delta + \alpha\beta}{2\gamma\delta - \alpha\beta} = \dfrac{2{a}^{2}{r}^{5} + {a}^{2}r}{2{a}^{2}{r}^{5} - {a}^{2}r} = \dfrac{2{r}^{4} + 1}{2{r}^{4} - 1} = \dfrac{8 + 1}{8 - 1} = \dfrac{9}{7}

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