Solving Inequalities: 0<(2x+1)(x-2) or 0>(2x+1)(x-2)?

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Discussion Overview

The discussion revolves around solving the inequality (4x-4)/(x+2)< 2x-3, which simplifies to analyzing the product (2x+1)(x-2) under different conditions based on the sign of x+2. Participants explore the implications of the product being greater than or less than zero and the intervals that satisfy the inequality.

Discussion Character

  • Mathematical reasoning
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant expresses uncertainty about their simplification to 0<(2x+1)(x-2) if x+2>0 and 0>(2x+1)(x-2) if x+2<0.
  • Another participant explains that the sign of a product depends on the signs of the factors and suggests checking intervals around the zeros of the function.
  • A participant claims to have found a solution of x>2 but is questioned about missing intervals.
  • Another participant provides a counterexample to the claimed solution, indicating that the interval -2

Areas of Agreement / Disagreement

Participants do not reach a consensus on the solution, as there are competing views regarding the intervals that satisfy the inequality and the correctness of the proposed solution x>2.

Contextual Notes

Participants reference the importance of identifying zeros and intervals but do not resolve the implications of their findings on the overall solution.

deryk
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Im trying to solve (4x-4)/(x+2)< 2x-3

I get it down to 0<(2x+1)(x-2) if x+2>0

0>(2x+1)(x-2) if x+2<0

Are these right so far? I am not sure what to do now with the product being bigger or smaller than 0. Thanks for your time.
 
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deryk said:
Im trying to solve (4x-4)/(x+2)< 2x-3

I get it down to 0<(2x+1)(x-2) if x+2>0

0>(2x+1)(x-2) if x+2<0

Are these right so far? I am not sure what to do now with the product being bigger or smaller than 0. Thanks for your time.
Right so far.
You have products
the sign of a product depends on the sighns of the factors
ab>0
means
a>0 and b>0
or
a>0 and b<0
ab<0
means
a>0 and b<0
or
a<0 and b>0

another way to think about it is (2x+1)(x-2) is a continuos function
find out where the zeros are
call them a and b with a<b
consider the intervals (since -2 is also an important number)
x<-2
-2<x<a
a<x<b
b<x
all the points in one of these intervals satisfy the inequality or none do
so checking one point in each intervals tells you if the whole interval satifies the inequality
 
Last edited:
thanks lurf lurf .I got x>2. Does anyone know if that's right?
 
deryk said:
thanks lurf lurf .I got x>2. Does anyone know if that's right?
you missed -2<x<-1/2
consider for example x=-1
(4x-4)/(x+2)< 2x-3
(4(-1)-4)/((-1)+2)< 2(-1)-3
(-4-4)/1<-2-3
-8<-5
 

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