Modulus got into Floor

Algebra Level 3

If x 2 , \left \lfloor |x| \right \rfloor \leq 2 ,

then x x belongs to:

Notations:

x x does not exist ( , 3 ) (-\infty , 3) None of the above [ 3 , 3 ] [-3 , 3] ( 3 , 3 ) (-3 , 3) ( 3 , ) (3 , \infty) Insufficient Information

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2 solutions

Sandeep Bhardwaj
Apr 30, 2016

We are given that x 2 \lfloor |x| \rfloor \leq 2 . Using the definition of floor function , we get

x < 3. |x|<3.

And now the above absolute value inequality gives us 3 < x < 3. -3<x<3.

Writing in the interval notation, we get x ( 3 , 3 ) . x \in (-3,3). \square

Simple and beautiful solution! :-)

akash patalwanshi - 5 years, 1 month ago

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Thank you. :-)

Sandeep Bhardwaj - 5 years, 1 month ago

Isnt the graph of this question amazing? V-shaped steps!

Ashish Menon - 5 years, 1 month ago
Silver Vice
May 1, 2016

A simple solution.

W e a r e g i v e n x 2 F i r s t w e b r e a k i t u p f r o m t h e i n s i d e . w e k n o w t h a t f o r t h a t x 2 x ( 2 , 2 ) N o t i c e t h e o p e n b r a c k e t s , t h e r e f o r e i t i m p l i e s t h a t 2 < x < 2 . B u t d u e t o t h e f l o o r f u n c t i o n , t h e v a l u e w i l l j u m p d o w n t o t h e l o w e r i n t e g e r . T h e r e f o r e t o a v o i d t h a t w e g o o n e i n t e g e r h i g h e r . i . e 3 , 3. x ( 3 , 3 ) We\quad are\quad given\\ \left\lfloor \left| x \right| \right\rfloor \quad \le \quad 2\\ First\quad we\quad break\quad it\quad up\quad from\quad the\quad inside.\\ we\quad know\quad that\quad for\quad that\quad \left| x \right| \quad \le \quad 2\\ x\quad \in \quad (-2,2)\\ Notice\quad the\quad open\quad brackets,\quad therefore\quad it\quad implies\\ that\quad -2\quad <\quad x\quad <\quad 2\quad .\\ But\quad due\quad to\quad the\quad floor\quad function,\quad the\quad value\quad will\quad \\ jump\quad down\quad to\quad the\quad lower\quad integer.\quad Therefore\quad to\\ avoid\quad that\quad we\quad go\quad one\quad integer\quad higher.\quad i.e\quad -3,3.\\ \quad \therefore \boxed { \quad x\quad \in \quad (-3,3)\quad } \quad \bigstar

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