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In the following example, given ∈ > 0, find a δ > 0 such that whenever, |x – a| < δ, we must have |f(x) – l| < ∈. limx→-3(3x+2) = – 7 - Mathematics and Statistics

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Question

In the following example, given ∈ > 0, find a δ > 0 such that whenever, |x – a| < δ, we must have |f(x) – l| < ∈.

`lim_(x -> -3) (3x + 2)` = – 7

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Solution

We have to find some δ so that

`lim_(x -> -3) (3x + 2)` = – 7 

Here a = – 3, l = 7 and f(x) = 3x + 2

Consider ∈ > 0 and |f(x) – l| < ∈

∴ |3x + 2 – (– 7)| < ∈

∴ |3x + 9| < ∈

∴ |3(x + 3)| < ∈

∴ `|x + 3| < ∈/3`

∴ `δ ≤ ∈/3` such that |x + 3| < δ ⇒ |f(x) + 7| < ∈

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Chapter 7: Limits - Exercise 7.1 [Page 139]

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