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Evaluate the following limit : limx→7[(x3-73)(x3+73)x-7]

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Question

Evaluate the following limit :

`lim_(x -> 7)[((root(3)(x) - root(3)(7))(root(3)(x) + root(3)(7)))/(x - 7)]`

Sum
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Solution

`lim_(x -> 7)[((root(3)(x) - root(3)(7))(root(3)(x) + root(3)(7)))/(x - 7)]`

= `lim_(x -> 7) ((root(3)(x))^2 - (root(3)(7))^2)/(x - 7)`

= `lim_(x -> 7) (x^(2/3) - 7^(2/3))/(x - 7)`

= `2/3(7)^(-1/3)      ...[because lim_(x -> "a") (x^"n" - "a"^"n")/(x - "a") = "na"^("n" - 1)]`

= `2/(3(root(3)(7))`.

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Chapter 7: Limits - Exercise 7.1 [Page 139]

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