Let f(x) = cos^-1(3x – 1). Then, dom (f) = ?

Question

Mark (√) against the correct answer in the following: 

Let f(x) = cos^-1(3x – 1). Then, dom (f) = ?

A. \((0, \frac{2}{3})\)

B. \([0,\frac{2}{3}]\)

C. \([\frac{-2}{3},\frac{2}{3}]\)

D. None of these

Answer 1

Correct Answer is (B) \([0,\frac{2}{3}]\)

f(x) = cos^-1(3x - 1). 

domain of cos^-1x = [ - 1,1] 

on multiplying by an integer the domain decreases by same number 

⇒ domain of cos^-13x = [ - 1/3,1/3] 

⇒ domain of cos^-1 (3x - 1) = [1/3 - 1/3,1/3 + 1/3] = [0,2/3]