Medium MCQ +4 / -1 PYQ · JEE Mains 2021

If the functions are defined as $f(x) = \sqrt x$ and $g(x) = \sqrt {1 - x}$, then what is the common domain of the following functions :

f + g, f $-$ g, f/g, g/f, g $-$ f where $(f \pm g)(x) = f(x) \pm g(x),(f/g)x = {{f(x)} \over {g(x)}}$

  1. A $0 \le x \le 1$
  2. B $0 \le x < 1$
  3. C $0 < x < 1$ Correct answer
  4. D $0 < x \le 1$

Solution

$f + g = \sqrt x + \sqrt {1 - x}$<br><br>$\Rightarrow x \ge 0$ &amp; $1 - x \ge 0 \Rightarrow x \in [0,1]$<br><br>$f - g = \sqrt x - \sqrt {1 - x}$<br><br>$\Rightarrow x \ge 0$ &amp; $1 - x \ge 0 \Rightarrow x \in [0,1]$<br><br>$f/g = {{\sqrt x } \over {\sqrt {1 - x} }}$<br><br>$\Rightarrow x \ge 0$ &amp; $1 - x &gt; 0 \Rightarrow x \in [0,1)$<br><br>$g/f = {{\sqrt {1 - x} } \over {\sqrt x }}$<br><br>$\Rightarrow 1 - x \ge 0$ &amp; $x &gt; 0 \Rightarrow x \in (0,1]$<br><br>$g - f = \sqrt {1 - x} - \sqrt x$<br><br>$\Rightarrow 1 - x \ge 0$ &amp; $x \ge 0 \Rightarrow x \in [0,1]$<br><br>$\Rightarrow$ $x \in (0,1)$

About this question

Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations

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