Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main 202125 FebruaryMorning Shift
Exam
JEE Main
Year
2021
Date
25 February
Shift
Morning Shift
Subject
Mathematics
Chapter
Quadratic Equation

JEE Main 2021 · 25 February · Morning Shift · Mathematics · Quadratic Equation

The integer k, for which the inequality x ^ 2 - 2(3k - 1)x + 8 k ^...

The integer k,k, for which the inequality x2−2(3k−1)x+8k2−7>0{x}^{2} - 2\left(3k - 1\right)x + 8{k}^{2} - 7 > 0 is valid for every xx in RR is:

Options

  1. A44
  2. B22
  3. C33
  4. D00

Correct answer

C. 33

Step-by-step solution

x2−2(3k−1)x+8k2−7>0{x}^{2} - 2\left(3k - 1\right)x + 8{k}^{2} - 7 > 0

Now, D<0D < 0

⇒4(3k−1)2−4×1×(8k2−7)<0⇒ 4{\left(3k - 1\right)}^{2} - 4 \times 1 \times \left(8{k}^{2} - 7\right) < 0

⇒9k2−6k+1−8k2+7<0⇒ 9{k}^{2} - 6k + 1 - 8{k}^{2} + 7 < 0

⇒k2−6k+8<0⇒ {k}^{2} - 6k + 8 < 0

⇒(k−4)(k−2)<0⇒ \left(k - 4\right)\left(k - 2\right) < 0

⇒k∈(2,4)⇒ k \in \left(2, 4\right)

⇒k=3⇒ k = 3

Practice Quadratic Equation on Quantrex Academy →

More from Quadratic Equation

Match each entry in List-I to the correct entry in List-II and choose the correct option.… JEE Advanced 2026Let a, b, c be positive integers in arithmetic progression such that the equation ax^2 +… JEE Advanced 2026Consider the quadratic equation (n^2 - 2n + 2)x^2 - 3x + (n^2 - 2n + 2)^2 = 0 , n ∈ ℝ .… JEE Main 2026Let one root of the quadratic equation in x : (k^2 - 15k + 27)x^2 + 9(k-1)x + 18 = 0 be… JEE Main 2026Let e_1 and e_2 be two distinct roots of the equation x^2 - ax + 2 = 0 . Let the sets \ a… JEE Main 2026Let α, β be the roots of the equation x^2 - x + p = 0 and γ, δ be the roots the equation… JEE Main 2026Let a, b ∈ ℂ . Let α, β be the roots of the equation x^2 + ax + b = 0 . If β - α = 11 and… JEE Main 2026Let A, B , where A, B ∈ (-(π)/(2), (π)/(2)) , be the roots of the quadratic equation x^2… JEE Main 2026If α=1 and β=1+i 2 , where i= -1 are two roots of the equation x^3+ax^2+bx+c=0 , a,b,c ∈… JEE Main 2026If the quadratic equation (λ+2)x^2-3λ x+4λ=0 , λ ≠ -2 , has two positive roots, then the… JEE Main 2026Let α, β be the roots of the equation x^2 - 3x + r = 0 , and (α)/(2), 2β be the roots of… JEE Main 2026Let a, b, c ∈ \ 1, 2, 3, 4\ . If the probability, that ax^2 + 2 2 \,bx + c > 0 for all x… JEE Main 2026Let S=\ x^ 3 +a x^ 2 +b x+c: a, b, c ∈ ~N. and .a, b, c ≤ 20\ be a set of polynomials.… JEE Main 2026If α, β , where α<β , are the roots of the equation λ x^ 2 -(λ+3) x+3=0 such that… JEE Main 2026The smallest positive integral value of a , for which all the roots of x^ 4 -a x^ 2 +9=0… JEE Main 2026The sum of all the real solutions of the equation _ (x+3) (6 x^ 2 +28 x+30)=5-2 _ (6… JEE Main 2026 Full Quadratic Equation list Quadratic Equation JEE Maths PYQsJEE Mathematics PYQs All JEE Main PYQs