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Evaluate the following : limx→1[x-1logx] - Mathematics and Statistics

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Question

Evaluate the following :

`lim_(x -> 1) [(sqrt(x) - 1)/logx]`

Sum

Solution

`lim_(x -> 1) (sqrt(x) - 1)/logx`

put x – 1 = h

∴ x = 1 + h

As x → 1, h → 0

∴ Required limit

= `lim_("h" -> 0) (sqrt(1 + "h") - 1)/(log(1 + "h"))`

= `lim_("h" -> 0) (sqrt(1 + "h") - 1)/(log (1 + "h")) xx (sqrt(1 + "h") + 1)/(sqrt(1 + "h") + 1)`

= `lim_("h" -> 0) ((1 + "h") - 1)/(log(1 + "h")) xx 1/(sqrt(1 + "h") + 1)`

= `lim_("h" -> 0) "h"/(log(1 + "h")) xx 1/(sqrt(1 + "h") + 1)`

= `lim_("h" -> 0) (1)/((log(1 + "h"))/("h")) xx 1/(sqrt(1 + "h") + 1)   ...[("Divide Numerator and"),("Denominator by h"),("As"  "h" -> 0","  "h" ≠ 0)]`

= `lim_("h" -> 0) (1)/((log(1 + "h"))/("h")) xx 1/(lim_("h" -> 0)(sqrt(1 + "h") + 1)` 

= `1/1 xx 1/(sqrt(1 + 0) + 1)`

= `1/2`

shaalaa.com
Substitution Method
  Is there an error in this question or solution?
Chapter 7: Limits - Miscellaneous Exercise 7.2 [Page 159]

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