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Evaluate the following limit : limx→0[(1-x)8-1(1-x)2-1]

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Question

Evaluate the following limit :

`lim_(x -> 0)[((1 - x)^8 - 1)/((1 - x)^2 - 1)]`

Sum
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Solution

Put 1 – x = y

Then as x → 0, y → 1

∴ `lim_(x -> 0) ((1 - x)^8 - 1)/((1 - x)^2 - 1)`

= `lim_(y -> 1) (y^8 - 1)/(y^2 - 1)`

= `lim_(y -> 1)[(((y^8 - 1)/(y - 1)))/(((y^2 - 1)/(y - 1)))]`  ...[∵ y → 1, y ≠ 1, ∴ y – 1 ≠ 0]

= `(lim_(y -> 1)((y^8 - 1)/(y - 1)))/(lim_(y -> 1)((y^2 - 1)/(y - 1))`

= `(8(1)^7)/(2(1)^1)     ...[because lim_(x -> "a") (x^"n" - "a"^"n")/(x - "a") = "na"^("n" - 1)]`

= 4

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Chapter 7: Limits - Exercise 7.1 [Page 139]

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