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Select the correct answer from the given alternatives: f(x) =(16x-1)(9x-1)(27x-1)(32x-1),for x≠0=k,for x=0 is continuous at x = 0, then ‘k’ =

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Question

Select the correct answer from the given alternatives:

f(x) `{:(= ((16^x - 1)(9^x - 1))/((27^x - 1)(32^x - 1))",", "for"  x ≠ 0),(= "k"",", "for"  x = 0):}` is continuous at x = 0, then ‘k’ =

Options

  • `8/3`

  • `8/15`

  • `-8/15`

  • `20/3`

MCQ
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Solution

`8/15`

Explanation:

f(x) is continuous at x = 0

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

`therefore "k" = lim_(x -> 0)((16^x - 1)(9^x - 1))/((27^x - 1)(32^x - 1))`

`= (lim_(x -> 0) ((16^x - 1)/x) xx lim_(x -> 0) ((9^x - 1)/x))/(lim_(x -> 0) ((27^x - 1)/x) xx lim_(x -> 0) ((32^x - 1)/x))`

`= (log 16 xx log 9)/(log 27 xx log 32)        ...[because  lim_(x -> 0) ("a"^x - 1)/x = log "a"]`

`= (4 log 2 xx 2 log 3)/(3 log 3 xx 5 log 2)`

`= (4 cancel(log 2) xx 2 cancel(log 3))/(3 cancel(log 3) xx 5 cancel(log 2))`

`= (4 xx 2)/(3 xx 5)`

`= 8/15`

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

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