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Check if the following function has an inverse function. If yes, find the inverse function. f(x) = 4x+5 - Mathematics and Statistics

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Question

Check if the following function has an inverse function. If yes, find the inverse function.

f(x) = `sqrt(4x + 5)`

Sum
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Solution

f(x) = `sqrt(4x + 5), x ≥ (-5)/4` 

Let f(x1) = (fx2)

∴ `sqrt(4x + 5) = sqrt(4x_2 + 5)`

∴ x1 = x2

∴ f is a one-one function.

f(x) =  `sqrt(4x + 5)` = y, say(y) ≥ 0

Squaring on both sides, we get

y2 = 4x + 5

∴ x = `(y^2 - 5)/4`

∴ For every y we can get x.

∴ f is an onto function.

∴ x = `(y^2 - 5)/4 = f^-1(y)`

Replacing y by x, we get

`f^-1(x) = (x^2 - 5)/4`

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Algebra of Functions
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Chapter 6: Functions - Exercise 6.2 [Page 128]

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