JEE Main202127 Aug 2021Evening ShiftMathematicsLimitsActual
If lim x → ∞ x 2 - x + 1 - a x = b , then the ordered pair ( a , b ) is:
Options
- A1 , - 1 2
- B- 1 , 1 2
- C- 1 , - 1 2
- D1 , 1 2
Correct answer
A. 1 , - 1 2
Step-by-step solution
Given that: lim x → ∞   x 2 − x + 1 − a x = b ⇒ lim x → ∞   x 2 − x + 1 − a x × x 2 − x + 1 + a x x 2 − x + 1 + a x = b ⇒ lim x → ∞   x 2 − x + 1 − ( a x ) 2 x 2 − x + 1 + a x = b ⇒  Limit exist only If  a 2 = 1 , because x 2 must not be there in the numerator ∴ a = 1 , − 1 ⇒ lim x → ∞   − x + 1 x 2 − x + 1 + a x = b ⇒ lim