JEE Main · 2021 · 20 Jul 2021 · Shift 1 · Quadratic Equations and Inequalities

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The probability of selecting integers such that , for all is :
  1. (A)✓ Correct
  2. (B)
  3. (C)
  4. (D)

Answer: (A)

Solution

A monic quadratic stays positive for every real exactly when its discriminant is negative:

Factorising, , so . The integers of that satisfy this are and , eight in all, while contains integers altogether. The probability is .

JEE Main · 2021 · 20 Jul 2021 · Shift 1 · Single correct option

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