Answer:
Since,
[tex]|x|=\left\{\begin{matrix}x &\text{ if } x \geq 0 \\ -x &\text{ if } x < 0\end{matrix}\right.[/tex]
Here, the given equation is,
|a| < b
Case 1 : if a ≥ 0,
|a| < b ⇒ a < b
Case 2 : If a < 0,
|a| < b ⇒ -a < b ⇒ a > - b
( Since, when we multiply both sides of inequality by negative number then the sign of inequality is reversed. )
|a| < b ⇒ a < b or a > - b ⇒ -b < a < b
Conversely,
If -b < a < b
⇒ a < b or a > - b
⇒ a < b or -a < b
⇒ |a| < b
Hence, proved..
