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Select the correct answer from the given alternatives: f(x) =32x-8x-4x+14x-2x+1+1,for x≠0=k,for x=0 is continuous at x = 0, then value of ‘k’ is

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Question

Select the correct answer from the given alternatives:

f(x) `{:(= (32^x - 8^x - 4^x + 1)/(4^x - 2^(x + 1) + 1)",", "for"  x ≠ 0),(= "k""," , "for"  x = 0):}` is continuous at x = 0, then value of ‘k’ is

Options

  • 6

  • 4

  • (log 2)(log 4)

  • 3 log 4

MCQ
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Solution

6

Explanation;

f(x) is continuous at x = 0

∴ f(0) = `lim_(x -> 0) "f"(x)`

∴ k = `lim_(x -> 0) (32^x - 8^x - 4^x + 1)/(4^x - 2^(x + 1) + 1)`

= `lim_(x -> 0) ((4^x - 1)(8^x - 1))/(2^x - 1)^2`

= `(lim_(x -> 0)((4^x - 1)/x)((8^x - 1)/x))/(lim_(x -> 0)((2^x - 1)/x)^2`

= `(lim_(x -> 0)((4^x - 1)/x) * lim_(x -> 0)((8^x - 1)/x))/((lim_(x -> 0) (2^x - 1)/x)^2`

= `(log4 xx log8)/(log2)^2`

= `(2log2 xx 3log2)/(log2)^2`

= 6

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

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