How to Solve an Inequality with Greatest Integer Function and Fractional Part?

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SUMMARY

The discussion focuses on solving the inequality \( x^2 \geq [x]^2 \), where \([x]\) represents the Greatest Integer Function and \(\{x\}\) denotes the Fractional Part. The solution involves manipulating the expression to \( x^2 - [x]^2 \geq 0 \) and factoring it as \((x + [x])(x - [x]) \geq 0\). The key conclusion is that the solution set for \(x\) is \( x \in (-\infty, -[x]] \cup [[x], \infty) \), clarifying the conditions under which the inequality holds.

PREREQUISITES
  • Understanding of the Greatest Integer Function (GIF)
  • Familiarity with the concept of Fractional Part
  • Basic algebraic manipulation and factoring techniques
  • Knowledge of inequalities and their solution sets
NEXT STEPS
  • Study the properties of the Greatest Integer Function and its applications
  • Learn about the Fractional Part and its significance in inequalities
  • Explore advanced algebraic techniques for solving polynomial inequalities
  • Investigate graphical methods for visualizing inequalities involving GIF and fractional parts
USEFUL FOR

Students and educators in mathematics, particularly those studying algebra and inequalities, as well as anyone interested in the applications of the Greatest Integer Function and Fractional Part in problem-solving.

utkarshakash
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Homework Statement


x^2 \geq [x]^2

[] denotes Greatest Integer Function
{} denotes Fractional Part

Homework Equations



The Attempt at a Solution



x^2-[x]^2 \geq 0 \\<br /> (x+[x])(x-[x]) \geq 0 \\<br /> -[x] \leq x \leq [x] \\<br />
Considering left inequality
<br /> x \geq -[x] \\<br /> \left\{x\right\} \geq -2[x]<br />
 
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utkarshakash said:

Homework Statement


x^2 \geq [x]^2

[] denotes Greatest Integer Function
{} denotes Fractional Part

Homework Equations



The Attempt at a Solution



x^2-[x]^2 \geq 0 \\<br /> (x+[x])(x-[x]) \geq 0
How do you go from the above step to the next step.

(It does look valid, but an explanation seems to be in order.)

-[x] \leq x \leq [x] \\<br />
Considering left inequality
<br /> x \geq -[x] \\<br /> \left\{x\right\} \geq -2[x]<br />
 
SammyS said:
How do you go from the above step to the next step.

(It does look valid, but an explanation seems to be in order.)

Ah! I made a silly mistake there. Actually it should be like this

x \in \left( -∞, -[x] \right] U \left[ [x],∞ \right)
 

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