The probability of selecting integers such that , for all is :
- (A)✓ Correct
- (B)
- (C)
- (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 .
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