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Solve | X + 1 | + | X | > 3 - Mathematics

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Question

Solve \[\left| x + 1 \right| + \left| x \right| > 3\] 

 

Solution

\[\text{ We have }, \left| x + 1 \right| + \left| x \right| > 3\]

\[\text{ As }, \left| x + 1 \right| = \binom{\left( x + 1 \right), x \geq - 1}{ - \left( x + 1 \right), x < - 1}\]

\[\text{ and } \left| x \right| = \binom{x, x \geq 0}{ - x, x < 0}\]

\[\text{ Case I: When } x < - 1, \]

\[\left| x + 1 \right| + \left| x \right| > 3\]

\[ \Rightarrow - \left( x + 1 \right) - x > 3\]

\[ \Rightarrow - 2x - 1 > 3\]

\[ \Rightarrow - 2x > 4\]

\[ \Rightarrow x < \frac{4}{- 2}\]

\[ \Rightarrow x < - 2\]

\[\text{ So }, x \in \left( - \infty , - 2 \right)\]

\[\text{ Case II: When } - 1 \leq x < 0, \]

\[\left| x + 1 \right| + \left| x \right| > 3\]

\[ \Rightarrow \left( x + 1 \right) - x > 3\]

\[ \Rightarrow 1 > 3, \text{ which is not possible }\]

\[\text{ So }, x \in \phi\]

\[\text{ Case III: When x } \geq 0, \]

\[\left| x + 1 \right| + \left| x \right| > 3\]

\[ \Rightarrow \left( x + 1 \right) + x > 3\]

\[ \Rightarrow 2x + 1 > 3\]

\[ \Rightarrow 2x > 2\]

\[ \Rightarrow x > \frac{2}{2}\]

\[ \Rightarrow x > 1\]

\[\text{ So }, x \in \left( 1, \infty \right)\]

\[\text{ From all the cases, we get }\]

\[x \in \left( - \infty , - 2 \right) \cup \left( 1, \infty \right)\]

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Chapter 15: Linear Inequations - Exercise 15.3 [Page 22]

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RD Sharma Mathematics [English] Class 11
Chapter 15 Linear Inequations
Exercise 15.3 | Q 11 | Page 22

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