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Evaluate the following limit: lim_(x -> 7)[((root(3)(x) - root(3)(7))(root(3)(x) + root(3)(7)))/(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)]`

Evaluate
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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)[((x^(1/3) - 7^(1/3))(x^(1/3) + 7^(1/3)))/(x - 7)]`

= `lim_(x -> 7)[(x^(2/3) - 7^(2/3))/(x - 7)]   ...[∵ (a  –  b)(a  +  b) = a^2  –  b^2]`

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

= `2/3(7)^(-1/3)`

= `2/3 × 1/7^(1/3)`

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

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Chapter 7: Limits - EXERCISE 7.1 [Page 100]

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