Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Quadratic Equation and Inequalities question

2020 · 4 Sep · Shift 2 · Q38
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Mathematics
  4. /Quadratic Equation and Inequalities
  5. /2020 · 4 Sep · Shift 2 · Q38

Quadratic Equation and Inequalities question

2020 · 4 Sep · Shift 2 · Q38

JEE MainMathematicsQuadratic Equation and InequalitiesMCQ+4 / −1
Let λe0\lambda e 0λe0 be in R. If α\alphaα and β\betaβ are the roots of the equation, x2 - x + 2 λ\lambdaλ= 0 and α\alphaα and γ\gammaγ are the roots of the equation, 3x2−10x+27λ=03{x^2} - 10x + 27\lambda = 03x2−10x+27λ=0, then βγλ{{\beta \gamma } \over \lambda }λβγ​ is equal to:
  1. A
    36
  2. B
    9
  3. C
    27
  4. D
    18
View written solutionFree

Correct answer: D

  1. Interpret the given equations

We are given:

  • α,β\alpha, \betaα,β are roots of x2−x+2λ=0x^2 - x + 2\lambda = 0x2−x+2λ=0
  • α,γ\alpha, \gammaα,γ are roots of 3x2−10x+27λ=03x^2 - 10x + 27\lambda = 03x2−10x+27λ=0

We need to find: βγλ\frac{\beta\gamma}{\lambda}λβγ​

Also, λ≠0\lambda \ne 0λ=0.


  1. Use sum of roots

For the first equation, x2−x+2λ=0x^2 - x + 2\lambda = 0x2−x+2λ=0 Sum of roots: α+β=1\alpha + \beta = 1α+β=1

For the second equation, 3x2−10x+27λ=03x^2 - 10x + 27\lambda = 03x2−10x+27λ=0 Sum of roots: α+γ=103\alpha + \gamma = \frac{10}{3}α+γ=310​

Subtracting, γ−β=103−1=73\gamma - \beta = \frac{10}{3} - 1 = \frac{7}{3}γ−β=310​−1=37​

But this alone is not enough. We now use product of roots.


  1. Use product of roots

For the first equation, αβ=2λ\alpha\beta = 2\lambdaαβ=2λ

For the second equation, αγ=27λ3=9λ\alpha\gamma = \frac{27\lambda}{3} = 9\lambdaαγ=327λ​=9λ

Now divide the second by the first: αγαβ=9λ2λ\frac{\alpha\gamma}{\alpha\beta} = \frac{9\lambda}{2\lambda}αβαγ​=2λ9λ​

Since λ≠0\lambda \ne 0λ=0 and α≠0\alpha \ne 0α=0 (otherwise αβ=2λ≠0\alpha\beta=2\lambda\ne 0αβ=2λ=0 impossible), we get γβ=92\frac{\gamma}{\beta} = \frac{9}{2}βγ​=29​

So, γ=92β\gamma = \frac{9}{2}\betaγ=29​β


  1. Use the relation from sums

We have α=1−β\alpha = 1-\betaα=1−β and also α=103−γ\alpha = \frac{10}{3} - \gammaα=310​−γ

Equating: 1−β=103−γ1-\beta = \frac{10}{3} - \gamma1−β=310​−γ γ−β=73\gamma - \beta = \frac{7}{3}γ−β=37​

Substitute γ=92β\gamma = \frac{9}{2}\betaγ=29​β: 92β−β=73\frac{9}{2}\beta - \beta = \frac{7}{3}29​β−β=37​ 72β=73\frac{7}{2}\beta = \frac{7}{3}27​β=37​ β=23\beta = \frac{2}{3}β=32​

Hence, γ=92⋅23=3\gamma = \frac{9}{2}\cdot \frac{2}{3} = 3γ=29​⋅32​=3


  1. Find λ\lambdaλ

From α+β=1\alpha + \beta = 1α+β=1 we get α=1−23=13\alpha = 1 - \frac{2}{3} = \frac{1}{3}α=1−32​=31​

Now use αβ=2λ\alpha\beta = 2\lambdaαβ=2λ 13⋅23=2λ\frac{1}{3}\cdot \frac{2}{3} = 2\lambda31​⋅32​=2λ 29=2λ\frac{2}{9} = 2\lambda92​=2λ λ=19\lambda = \frac{1}{9}λ=91​


  1. Compute the required value

βγλ=(23)(3)1/9=21/9=18\frac{\beta\gamma}{\lambda} = \frac{\left(\frac{2}{3}\right)(3)}{1/9} = \frac{2}{1/9} = 18λβγ​=1/9(32​)(3)​=1/92​=18


  1. Check options

The value is 181818 So the correct option is D.

PreviousNext

More from Quadratic Equation and Inequalities

  • The product of the roots of the equation 9x2 - 18|x| + 5 = 0 is :2020 · MCQ
  • If α and β are the roots of the equation, 7x2 – 3x – 2 = 0, then the value of 1−α2α​+1−β2β​ is equal to :2020 · MCQ
  • If α and β be two roots of the equation x2 – 64x + 256 = 0. Then the value of (β5α3​)1/8+(α5β3​)1/8 is :2020 · MCQ
  • If α and β are the roots of the equation 2x(2x + 1) = 1, then β is equal to :2020 · MCQ
  • Let α and β be two real roots of the equation (k + 1)tan2x -2​. λ tanx = (1 - k), where k(e - 1) and λ are real numbers. if tan2 (α+β) = 50, then a value of λ is:2020 · MCQ
  • Let α and β be the roots of the equation x2 - x - 1 = 0. If pk =(α)k+(β)k, k ≥ 1, then which one of the following statements is not true?2020 · MCQ
  • The least positive value of 'a' for which the equation 2x2 + (a – 10)x + 233​ = 2a has real roots is2020 · Numerical
  • Let α=2−1+i3​​. If a=(1+α)k=0∑100​α2k and b=k=0∑100​α3k, then a and b are the roots of the quadratic equation :2020 · MCQ