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Let f: R → R be the function defined by f(x) = 12-cosx ∀ x ∈ R.Then, find the range of f - Mathematics

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Question

Let f: R → R be the function defined by f(x) = `1/(2 - cosx)` ∀ x ∈ R.Then, find the range of f

Sum

Solution

Given,

f(x) = `1/(2 - cos x)` ∀ x ∈ R

Let y = `1/(2 - cos x)` 

2y – ycos x = 1

cos x = `(2y - 1)/y`

cos x = `(2 - 1)/y`

Now, we know that –1 ≤ cos x ≤ 1

So,

–1 ≤ 2 – `1/(y ≤ 1)`

–3 ≤ – `1/(y ≤ -1)`

1 ≤ – `1/(y ≤ 3)`

`1/3` ≤ y ≤ 1

Thus, the range of the given function is `[1/3, 1]`.

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Chapter 1: Relations And Functions - Exercise [Page 12]

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NCERT Exemplar Mathematics [English] Class 12
Chapter 1 Relations And Functions
Exercise | Q 14 | Page 12
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