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Evaluate the following limit : limx→3[2x+3-4x-3x2-9] - Mathematics and Statistics

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Question

Evaluate the following limit :

`lim_(x -> 3)[(sqrt(2x + 3) - sqrt(4x - 3))/(x^2 - 9)]`

Sum

Solution

`lim_(x -> 3)[(sqrt(2x + 3) - sqrt(4x - 3))/(x^2 - 9)]`

`lim_(x -> 3)[(sqrt(2x + 3) - sqrt(4x - 3))/(x^2 - 9) xx (sqrt(2x + 3) + sqrt(4x - 3))/(sqrt(2x + 3) + sqrt(4x - 3))]`

= `lim_(x -> 3) [((2x + 3) - (4x - 3))/((x^2 - 9)(sqrt(2x + 3) + sqrt(4x - 3)))]`

= `lim_(x -> 3) [(-2x + 6)/((x^2 - 9)(sqrt(2x + 3) + sqrt(4x - 3)))]`

= `lim_(x -> 3)[(-2(x - 3))/((x + 3)(x - 3)(sqrt(2x + 3) + sqrt(4x - 3)))]`

= `lim_(x -> 3)[(-2)/((x + 3)(sqrt(2x + 3) + sqrt(4x - 3)))]`  ...[∵ x → 3, ∴ x ≠ 3, ∴ x – 3 ≠ 0]

= `(-2)/((3 + 3)(sqrt(2(3) + 3) + sqrt(4(3) - 3))` 

= `(-2)/(6(3 + 3))`

= `(-1)/(18)`

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Rationalization Method
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Chapter 7: Limits - Exercise 7.3 [Page 143]

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