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Evaluate the following limits: limz→4[3-5+z1-5-z] - Mathematics and Statistics

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Question

Evaluate the following limits: `lim_(z -> 4) [(3 - sqrt(5 + z))/(1 - sqrt(5 - z))]`

Sum

Solution

`lim_(z -> 4) [(3 - sqrt(5 + z))/(1 - sqrt(5 - z))]`

= `lim_(z -> 4)[(3 - sqrt(5 + z))/(1 - sqrt(5 - z)) xx (3 + sqrt(5 + z))/(1 + sqrt(5 - z)) xx (1 + sqrt(5 - z))/(3 + sqrt(5 + z))]`

= `lim_(z -> 4)[(9 - (5 + z))/(1 - (5 - z)) xx (1 + sqrt(5 - z))/(3 + sqrt(5 + z))]`

= `lim_(z -> 4)[(4 - z)/(-4 + z) xx (1 + sqrt(5 - z))/(3 + sqrt(5 + z))]`

= `lim_(z -> 4)[(-(z - 4))/(z - 4) xx (1 + sqrt(5 - z))/(3 + sqrt(5 + z))]`

= `lim_(z -> 4) [(-1 + sqrt(5 - z))/(3 + sqrt(5 + z))]   ...[(because z -> 4"," therefore z ≠ 4","),(therefore z - 4 ≠0)]`

= `(-(1 + sqrt(5 - 4)))/(3 + sqrt(5 + 4)`

= `(-(1 + 1))/(3 + 3)`

= `(-2)/6`

= `-1/3`

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

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