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QJEEM21Maa91e: JEE Main 2021 Mathematics - Class 12 JEEM21Maa91e Solution: Let f : R R be a function such that f(2) = 4 and f'(2) = 1.…

Let f : R →\to R be a function such that f(2) = 4 and f'(2) = 1. Then, the value of lim⁡x→2x2f(2)−4f(x)x−2\mathop {\lim }\limits_{x \to 2} {{{x^2}f(2) - 4f(x)} \over {x - 2}} is equal to :

Multiple Choice Options

  • A 4
  • B 8
  • C 16
  • D 12

Step-by-Step Verified Solution

This limit can be solved using L'Hopital's Rule, which states that for the limit of the form 0/0 or ±∞/±∞, the limit can be found by taking the derivative of the numerator and the derivative of the denominator separately.

lim⁡x→2x2f(2)−4f(x)x−2\mathop {\lim }\limits_{x \to 2} {{{x^2}f(2) - 4f(x)} \over {x - 2}} is in the indeterminate form, and we are given that f(2) = 4 and f'(2) = 1, so we can apply L'Hopital's rule.

Taking the derivative of the numerator and the denominator, we get :

Numerator: derivative of x2f(2)−4f(x)x^2 f(2) - 4f(x) is 2xf(2)−4f′(x)2x f(2) - 4f'(x) .

Denominator: derivative of x−2x - 2 is 11 .

So, the limit becomes :

lim⁡x→22xf(2)−4f′(x)1=2×2×f(2)−4×f′(2)=16−4=12.\mathop {\lim }\limits_{x \to 2} {{{2xf(2) - 4f'(x)}} \over 1} = 2 \times 2 \times f(2) - 4 \times f'(2) = 16 - 4 = 12.

Therefore, Option D, 12, is the correct answer.

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