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Evaluate the following: limx→0[9x-5x4x-1] - Mathematics and Statistics

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Question

Evaluate the following: `lim_(x -> 0)[(9^x - 5^x)/(4^x - 1)]`

Sum

Solution

`lim_(x -> 0)(9^x - 5^x)/(4^x - 1)`

= `lim_(x -> 0) (9^x - 1 + 1 - 5^x)/(4^x - 1)`

= `lim_(x -> 0) ((9^x - 1) - (5^x - 1))/(4^x - 1)`

= `lim_(x -> 0) ((9^x - 1 - 5^x - 1)/x)/((4^x - 1)/x`   ...[∵ x → 0, ∴ x ≠ 0]

= `lim_(x -> 0) (((9^x - 1)/x) - ((5^x - 1)/x))/(((4^x - 1)/x)`

= `(lim_(x -> 0) (9^x - 1)/x - lim_(x -> 0) (5^x - 1)/x)/(lim_(x -> 0) (4^x - 1)/x)`

= `(log9 - log5)/(log4)   ...[because  lim_(x -> 0) ("a"^x - 1)/x = log "a"]`

= `1/(log4)log(9/5)`

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Limits of Exponential and Logarithmic Functions
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Chapter 7: Limits - EXERCISE 7.4 [Page 105]
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