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Modulus Function, Properties of Modulus Function - (Concept)

Modulus Function:

The function f: R\small \rightarrowR defined by f(x) = |x| for each x \small \in R is called the modulus function.

For each non-negative value of x, f(x) is equal to x. But for negative values of x, the value of f(x) is the negative of the value of x

$|\mathrm{x}|, \quad \mathrm{x} \in \mathbb{R}=\left\{\begin{array}{cc}x, & x \geq 0 \\ -x, & x<0\end{array}\right.$

Range $\in[0, \infty)$

Modulus Equations: Properties

If $a>0$
1. $|x|=a$, then $x=a,-a$
2. $|x|=|-x|$
3. $|x|^2=x^2$
4. If $|\mathrm{x}|=\mathrm{x}$, then $\mathrm{x}>0$ or $\mathrm{x}=0$
5. If $|x|=-x$, then $x<0$ or $x=0$
6. $|f(x)|=|g(x)|$, then $f(x)=g(x)$ or $f(x)=-g(x)$

Modulus inequalities

These deal with the inequalities (<, >, ≤, ≥ ) on expressions with absolute value sign. 

Properties

If a, b > 0, then

1.
$
\begin{aligned}
& |x| \leq a \Rightarrow x^2 \leq a^2 \\
& \Rightarrow-a \leq x \leq a
\end{aligned}
$
2.
$
\begin{aligned}
& |x| \geq a \Rightarrow x^2 \geq a^2 \\
& \Rightarrow x \leq-a \text { or } x \geq a
\end{aligned}
$
3.
$
\begin{aligned}
& a \leq|x| \leq b \Rightarrow a^2 \leq x^2 \leq b^2 \\
& \Rightarrow x \in[-b,-a] \cup[a, b]
\end{aligned}
$
4. $|x+y|=|x|+|y| \Leftrightarrow x y \geq 0$.
5. $|x-y|=|x|-|y| \Rightarrow x \cdot y \geq 0$ and $|x| \geq|y|$
6. $|x \pm y| \leq|x|+|y|$
7. $|x \pm y| \geq||x|-|y||$

Exam Chapter
JEE MAIN Sets, Relations and Functions
Mathematics Textbook for Class XI
Page No. : 41
Line : 3

 The Modulus function The function f: R\small \rightarrowR defined by f(x) = |x| for each  x \small \in R is called modulus function. For each
non-negative value of x, f(x) is equal to x.

But for negative values of x, the value of  f(x) is the negative of the value of x, 


Differential Calculus (Arihant)
Page No. : 111
Line : 1

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