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Evaluate the following : limx→∞[x3+3x+2(x+4)(x-6)(x-3)] - Mathematics and Statistics

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Question

Evaluate the following :

`lim_(x -> ∞) [(x^3 + 3x + 2)/((x + 4)(x - 6)(x - 3))]`

Sum

Solution

Let L = `lim_(x -> ∞) [(x^3 + 3x + 2)/((x + 4)(x - 6)(x - 3))]`

Dividing numerator and denominator by x3, we get, 

L = `lim_(x -> ∞) (1 + 3/x^2 + 2/x^3)/(((x + 4)/x)((x - 6)/x)((x - 3)/x)`

= `lim_(x -> ∞) (1 + 3/x^2 + 2/x^3)/((1 + 4/x)(1 - 6/x)(1 - 3/x))`

= `(lim_(x -> ∞)[1 + 3 xx 1/x^2 + 2 xx 1/x^3])/([lim_(x -> ∞) (1 + 4 xx 1/x)] xx [lim_(x -> ∞) (1 - 6 xx 1/x)] xx [lim_(x -> ∞) (1 - 3 xx 1/x)])`

= `(1 + 3 xx 0 + 2 xx 0)/([1 + 4 xx 0] xx [1 - 6 xx 0] xx [ 1 - 3 xx 0])  ...[because  lim_(x -> ∞) 1/x^"n" = 0  "if n" > 0]`

= 1

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