Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main 20262 AprilMorning Shift
Exam
JEE Main
Year
2026
Date
2 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Quadratic Equation

JEE Main 2026 · 2 April · Morning Shift · Mathematics · Quadratic Equation

Let a, b, c ∈ \ 1, 2, 3, 4\ . If the probability, that ax^2 + 2 2...

Let a,b,c∈{1,2,3,4}a, b, c \in \{1, 2, 3, 4\}. If the probability, that ax2+22 bx+c>0ax^2 + 2\sqrt{2}\,bx + c > 0 for all x∈Rx \in \mathbb{R}, is mn\dfrac{m}{n}, gcd⁡(m,n)=1\gcd(m, n) = 1, then m+nm + n is equal to _______.

Correct answer

0

Step-by-step solution

For the quadratic expression ax2+22bx+c>0ax^2 + 2\sqrt{2}bx + c > 0 for all x∈Rx \in \mathbb{R}, the leading coefficient must be positive and the discriminant must be negative.

Since a∈{1,2,3,4}a \in \{1, 2, 3, 4\}, the condition a>0a > 0 is always satisfied.

The discriminant condition is:
D<0D < 0
⇒(22b)2−4ac<0\Rightarrow (2\sqrt{2}b)^2 - 4ac < 0
⇒8b2−4ac<0\Rightarrow 8b^2 - 4ac < 0
⇒2b2<ac\Rightarrow 2b^2 < ac

The total number of possible triplets (a,b,c)(a, b, c) is 4×4×4=644 \times 4 \times 4 = 64.

Now, we find the number of favorable outcomes by checking the possible values of b∈{1,2,3,4}b \in \{1, 2, 3, 4\}:

Case 1: b=1b = 1
We need 2(1)2<ac⇒ac>22(1)^2 < ac \Rightarrow ac > 2.
The total number of pairs (a,c)(a, c) is 4×4=164 \times 4 = 16.
The pairs for which ac≤2ac \le 2 are (1,1),(1,2),(2,1)(1, 1), (1, 2), (2, 1), which are 33 in number.
So, the number of pairs with ac>2ac > 2 is 16−3=1316 - 3 = 13.

Case 2: b=2b = 2
We need 2(2)2<ac⇒ac>82(2)^2 < ac \Rightarrow ac > 8.
The possible pairs (a,c)(a, c) from the given set are (3,3),(3,4),(4,3),(4,4)(3, 3), (3, 4), (4, 3), (4, 4).
So, there are 44 pairs.

Case 3: b=3b = 3
We need 2(3)2<ac⇒ac>182(3)^2 < ac \Rightarrow ac > 18.
Since the maximum possible value of acac is 4×4=164 \times 4 = 16, there are 00 pairs.

Case 4: b=4b = 4
We need 2(4)2<ac⇒ac>322(4)^2 < ac \Rightarrow ac > 32.
Again, there are 00 pairs.

Total number of favorable outcomes = 13+4=1713 + 4 = 17.

The required probability is mn=1764\dfrac{m}{n} = \dfrac{17}{64}.

Since gcd⁡(17,64)=1\gcd(17, 64) = 1, we have m=17m = 17 and n=64n = 64.

Therefore, m+n=17+64=81m + n = 17 + 64 = 81.

Answer: 8181
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 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 2026A building construction work can be completed by two masons A and B together in 22.5… JEE Main 2026 Full Quadratic Equation list Quadratic Equation JEE Maths PYQsJEE Mathematics PYQs All JEE Main PYQs