Question:

Domain of the function $f (x) = \log_x \; \cos \; x$, is

Updated On: Sep 3, 2024
  • $\left( - \frac{\pi}{2} , \frac{\pi}{2}\right) - \left\{1\right\} $
  • $\left[ - \frac{\pi}{2} , \frac{\pi}{2}\right] - \left\{1\right\} $
  • $\left( - \frac{\pi}{2} , \frac{\pi}{2}\right) $
  • $None\, of\, these$
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The Correct Option is D

Solution and Explanation

We have the function $f(x)=\log _{x} \cos x$ $f(x)$ is defined for $\cos x>0$, $x >0, x \neq 1$ $\because \cos x >0$ $\Rightarrow -\frac{\pi}{2} < x < \frac{\pi}{2}$ Also, $x > 0, x \neq 1$ $\therefore$ Domain of $f$ is $\left(0, \frac{\pi}{2}\right)-\{1\}$.
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Concepts Used:

Relations and functions

A relation R from a non-empty set B is a subset of the cartesian product A × B. The subset is derived by describing a relationship between the first element and the second element of the ordered pairs in A × B.

A relation f from a set A to a set B is said to be a function if every element of set A has one and only one image in set B. In other words, no two distinct elements of B have the same pre-image.

Representation of Relation and Function

Relations and functions can be represented in different forms such as arrow representation, algebraic form, set-builder form, graphically, roster form, and tabular form. Define a function f: A = {1, 2, 3} → B = {1, 4, 9} such that f(1) = 1, f(2) = 4, f(3) = 9. Now, represent this function in different forms.

  1. Set-builder form - {(x, y): f(x) = y2, x ∈ A, y ∈ B}
  2. Roster form - {(1, 1), (2, 4), (3, 9)}
  3. Arrow Representation