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Evaluate the following limits: limx→4[x2+x-203x+4-4] - Mathematics and Statistics

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Question

``Evaluate the following limits: `lim_(x -> 4) [(x^2 + x - 20)/(sqrt(3x + 4) - 4)]`

Sum

Solution

`lim_(x -> 4) [(x^2 + x - 20)/(sqrt(3x + 4) - 4)]`

= `lim_(x -> 4) [((x + 5)(x - 4))/(sqrt(3x + 4) - 4) xx(sqrt(3x + 4) + 4)/(sqrt(3x + 4) + 4)]`

= `lim_(x -> 4) ((x + 5)(x - 4)(sqrt(3x + 4) + 4))/(3x + 4 - 16)`

= `lim_(x -> 4) ((x + 5)(x - 4)(sqrt(3x + 4) + 4))/(3x - 12)`

= `lim_(x -> 4) ((x + 5)(x - 4)(sqrt(3x + 4) + 4))/(3(x - 4)`

= `lim_(x -> 4) ((x - 5)(sqrt(3x + 4) + 4))/3   ...[(because x ->4"," x ≠ 4),(therefore x - 4 ≠ 0)]`

= `((4 + 5)(sqrt(3(4) + 4) + 4))/3`

= `(9(4 + 4))/3`

= 3(8)
= 24

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Rationalization Method
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Chapter 7: Limits - EXERCISE 7.3 [Page 103]

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