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Select the correct answer from the given alternatives: If f(x) = 12x-4x-3x+11-cos2x, for x ≠ 0 is continuous at x = 0 then the value of f(0) is ______.

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Question

Select the correct answer from the given alternatives:

If f(x) = `(12^x - 4^x - 3^x + 1)/(1 - cos 2x)`, for x ≠ 0 is continuous at x = 0 then the value of f(0) is ______.

Options

  • `log12/2`

  • log2.log3

  • `(log2*log3)/2`

  • None of these.

MCQ
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Solution

If f(x) = `(12^x - 4^x - 3^x + 1)/(1 - cos 2x)`, for x ≠ 0 is continuous at x = 0 then the value of f(0) is log 2 · log 3.

Explanation:

If f(x) is continuous at x = 0 (given)

`therefore "f"(0) = lim_(x -> 0) "f"(x)`

`= lim_(x -> 0) (12^x - 4^x - 3^x + 1)/(1 - cos 2x)`

`= 1/2 lim_(x ->0) (4^x (3^x - 1)(3^x - 1))/(sin^2 x)`

`= 1/2 lim_(x -> 0) ((3^x - 1)(4^x - 1))/(sin^2 x)`

`= 1/2 (lim_(x -> 0) ((3^x - 1)/x) * lim_(x - > 0) ((4^x - 1)/x))/(lim_(x -> 0) (sin x)/x)^2`

`= 1/2 xx ((log 3) xx (log 4))/(1)^2`

`= 1/2 xx log 3 xx log (2)^2`

= log 3 · log 2

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Chapter 8: Continuity - MISCELLANEOUS EXERCISE-8 [Page 176]

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