Let f : R → R be a function whose inverse is \(\rm \frac {x+5}{3}\). What is f(x) equal to?

  1. f(x) = 3x + 5
  2. f(x) = 3x - 5
  3. f(x) = 5x - 3
  4. f(x) = 5 - 3x
  5. f(x) does not exist

Answer (Detailed Solution Below)

Option 2 : f(x) = 3x - 5
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Detailed Solution

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Concept:

If y = f(x) then x = f-1 (y)

Calculations:

Given, f : R → R be a function whose inverse is \(\rm \frac {x+5}{3}\).

⇒ y = f-1 (x) =\(\rm \frac{x+5}{3}\)

⇒ 3y = x + 5

⇒ x = 3y - 5

⇒y = f-1 (x) 

⇒ x = f(y)

⇒ x = 3y - 5 = f(y)

⇒ f(y) = 3y - 5

⇒f(x) = 3x - 5

Hence, let  f : R → R be a function whose inverse is \(\rm \frac {x+5}{3}\). then f(x) = 3x - 5 

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