Inequality b*(b-4)<-4a is there a way to find the restrictions

  • Thread starter Thread starter Nusc
  • Start date Start date
  • Tags Tags
    Inequality
Click For Summary

Discussion Overview

The discussion revolves around the inequality b*(b-4)<-4a and explores the restrictions on the variables a and b for which this inequality holds. Participants consider both graphical and algebraic approaches to analyze the quadratic nature of the inequality and its implications.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant suggests that the inequality can be transformed into a quadratic inequality and proposes graphing a = (-1/4)(b^2 - 4b) to identify the solution set.
  • Another participant raises a question about satisfying an additional inequality, b^2/a^2-2*b/a+2*b+1-2*a+a^2 > 0, along with the condition a-b < 0.
  • Further, a participant questions the feasibility of certain conditions, specifically b < a-a^2 and a+a^2 < b.
  • One participant expresses uncertainty about the possibility of satisfying the inequalities presented.

Areas of Agreement / Disagreement

The discussion includes multiple competing views and remains unresolved, particularly regarding the additional inequalities and their implications on the original inequality.

Contextual Notes

Participants do not fully resolve the mathematical steps or the implications of the additional inequalities, leaving some assumptions and dependencies unclear.

Nusc
Messages
752
Reaction score
2
Mathematica or Maple

If I have an inequality b*(b-4)<-4a is there a way to find the restrictions on a and b for which inequality holds?
 
Physics news on Phys.org


This can be done without Mathematica or Maple.

b(b - 4) < -4a <==> (-1/4)b(b - 4) > a

This is a quadratic inequalilty. To find the solution set, graph a = (-1/4)(b^2 - 4b). The graph is a parabola that opens down. The graph of the parabola isn't in the solution set, but one side or another (i.e., either the inside or outside) of the parabola represents the solution set.

To determine which side is the solution set, simply pick any point that is not on the graph of the parabola. If the original inequality is a true statement for that point, the solution set is all of the points on that side of the parabola. If the original inequality is not a true statement for that point, the solution set is all of the points on the other side.
 


What if I had to satisfy another inequality?

b^2/a^2-2*b/a+2*b+1-2*a+a^2 > 0, a-b < 0
 
Last edited:


Wait, is this ever possible?

b < a-a^2, a+a^2 < b ?
 


Nevermind.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
Replies
2
Views
2K
Replies
8
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
Replies
1
Views
2K
Replies
6
Views
4K