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

2021 · 26 Aug · Shift 2 · Q43
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. /2021 · 26 Aug · Shift 2 · Q43

Quadratic Equation and Inequalities question

2021 · 26 Aug · Shift 2 · Q43

JEE MainMathematicsQuadratic Equation and InequalitiesNumerical+4 / −1
Let λe\lambda eλe 0 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 equation 3x2 −-− 10x + 27 λ\lambdaλ= 0, then βγλ{{\beta \gamma } \over \lambda }λβγ​ is equal to ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 18

We are given:

  1. α,β\alpha,\betaα,β are roots of x2−x+2λ=0x^2-x+2\lambda=0x2−x+2λ=0

  2. 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​.


1. Use Vieta's formulas for the first equation

For x2−x+2λ=0,x^2-x+2\lambda=0,x2−x+2λ=0, if roots are α,β\alpha,\betaα,β, then α+β=1,αβ=2λ.\alpha+\beta=1, \qquad \alpha\beta=2\lambda.α+β=1,αβ=2λ.

Hence, β=1−α.\beta=1-\alpha.β=1−α.


2. Use Vieta's formulas for the second equation

For 3x2−10x+27λ=0,3x^2-10x+27\lambda=0,3x2−10x+27λ=0, if roots are α,γ\alpha,\gammaα,γ, then α+γ=103,αγ=27λ3=9λ.\alpha+\gamma=\frac{10}{3}, \qquad \alpha\gamma=\frac{27\lambda}{3}=9\lambda.α+γ=310​,αγ=327λ​=9λ.

Hence, γ=103−α.\gamma=\frac{10}{3}-\alpha.γ=310​−α.


3. Since α\alphaα is common, it satisfies both equations

So α\alphaα must satisfy: α2−α+2λ=0and3α2−10α+27λ=0.\alpha^2-\alpha+2\lambda=0 \quad \text{and} \quad 3\alpha^2-10\alpha+27\lambda=0.α2−α+2λ=0and3α2−10α+27λ=0.

From the first equation, 2λ=−α2+α2\lambda=-\alpha^2+\alpha2λ=−α2+α so λ=α−α22.\lambda=\frac{\alpha-\alpha^2}{2}. λ=2α−α2​.

Substitute into the second equation: 3α2−10α+27(α−α22)=0.3\alpha^2-10\alpha+27\left(\frac{\alpha-\alpha^2}{2}\right)=0.3α2−10α+27(2α−α2​)=0.

Multiply by 222: 6α2−20α+27α−27α2=0.6\alpha^2-20\alpha+27\alpha-27\alpha^2=0.6α2−20α+27α−27α2=0.

−21α2+7α=0.-21\alpha^2+7\alpha=0.−21α2+7α=0.

7α(−3α+1)=0.7\alpha(-3\alpha+1)=0.7α(−3α+1)=0.

So, α=0orα=13.\alpha=0 \quad \text{or} \quad \alpha=\frac13.α=0orα=31​.

But the question states λ≠0\lambda\ne 0λ=0.

If α=0\alpha=0α=0, then from λ=α−α22,\lambda=\frac{\alpha-\alpha^2}{2},λ=2α−α2​, we get λ=0\lambda=0λ=0, not allowed.

Therefore, α=13.\alpha=\frac13.α=31​.


4. Find β,γ,\beta,\gamma,β,γ, and λ\lambdaλ

From α+β=1,\alpha+\beta=1,α+β=1, β=1−13=23.\beta=1-\frac13=\frac23.β=1−31​=32​.

From α+γ=103,\alpha+\gamma=\frac{10}{3},α+γ=310​, γ=103−13=3.\gamma=\frac{10}{3}-\frac13=3.γ=310​−31​=3.

From αβ=2λ,\alpha\beta=2\lambda,αβ=2λ, 13⋅23=2λ\frac13\cdot\frac23=2\lambda31​⋅32​=2λ 29=2λ\frac{2}{9}=2\lambda92​=2λ λ=19.\lambda=\frac19.λ=91​.


5. Compute the required value

βγλ=(23)(3)1/9.\frac{\beta\gamma}{\lambda}=\frac{\left(\frac23\right)(3)}{1/9}.λβγ​=1/9(32​)(3)​.

First, (23)(3)=2.\left(\frac23\right)(3)=2.(32​)(3)=2.

So, βγλ=21/9=18.\frac{\beta\gamma}{\lambda}=\frac{2}{1/9}=18.λβγ​=1/92​=18.


Final Answer

18\boxed{18}18​

The derived answer matches the stored correct answer.

PreviousNext

More from Quadratic Equation and Inequalities

  • The sum of 162th power of the roots of the equation x3 − 2x2 + 2x − 1 = 0 is ​.2021 · Numerical
  • Let α and β be two real numbers such that α+β= 1 and αβ=− 1. Let pn = (α)n + (β)n, pn − 1 = 11 and pn+1 = 29 for some integer n ≥ 1. Then, the value of p n2​ is ​…2021 · Numerical
  • The set of all values of K > − 1, for which the equation (3x2+4x+3)2−(k+1)(3x2+4x+3)(3x2+4x+2)+k(3x2+4x+2)2=0 has real roots, is :2021 · MCQ
  • Let α, β be two roots of the equation x2 + (20)1/4x + (5)1/2 = 0. Then α 8 + β 8 is equal to2021 · MCQ
  • Let α=x∈Rmax​{82sin3x.44cos3x} and β=x∈Rmin​{82sin3x.44cos3x}. If 8x2+bx+c=0 is a quadratic equation whose roots are α…2021 · MCQ
  • The number of real roots of the equation e4x − e3x − 4e2x − ex + 1 = 0 is equal to ​.2021 · Numerical
  • cosec18 ∘ is a root of the equation :2021 · MCQ
  • The sum of the roots of the equation x+1−2log2​(3+2x)+2log4​(10−2−x)=0, is :2021 · MCQ