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Evaluate the following : limx→∞[x(x+1-x)] - Mathematics and Statistics

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Question

Evaluate the following :

`lim_(x -> ∞) [sqrt(x)(sqrt(x + 1) - sqrt(x))]`

Sum

Solution

`lim_(x -> ∞) [sqrt(x)(sqrt(x + 1) - sqrt(x))]`

= `lim_(x -> ∞) sqrt(x) (sqrt(x + 1) - sqrt(x)) xx ((sqrt(x + 1)  + sqrt(x)))/(sqrt(x + 1) + sqrt(x))`

= `lim_(x -> ∞) (sqrt(x)(x + 1 - x))/(sqrt(x + 1) + sqrt(x))`

= `lim_(x -> ∞) (sqrt(x))/(sqrt(x + 1) + sqrt(x))`

= `lim_(x -> ∞) 1/((sqrt(x + 1))/(sqrt(x)) + 1)  ...[("Divide numerator and"),("denominator by"  sqrt(x))]`

= `lim_(x -> ∞) 1/(sqrt((x + 1)/x) + 1)`

= `1/(lim_(x -> ∞)(sqrt(1 + 1/x ) + 1))`

= `1/(sqrt(1 + 0) + 1)  ...[lim_(x -> ∞) 1/x^"k" = 0, "k" > 0]`

= `1/(1 + 1)`

= `1/2`

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Limit at Infinity
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Chapter 7: Limits - Exercise 7.7 [Page 157]
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