Solving inequalties

  • Thread starter deryk
  • Start date
10
0

Main Question or Discussion Point

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? Im not sure what to do now with the product being bigger or smaller than 0. Thanks for your time.
 

Answers and Replies

lurflurf
Homework Helper
2,418
122
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? Im 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:
10
0
thanks lurf lurf .I got x>2. Does anyone know if that's right?
 
lurflurf
Homework Helper
2,418
122
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
 
Top