Solving inequalties

  • Thread starter deryk
  • Start date
  • #1
10
0
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

  • #2
lurflurf
Homework Helper
2,440
138
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:
  • #3
10
0
thanks lurf lurf .I got x>2. Does anyone know if that's right?
 
  • #4
lurflurf
Homework Helper
2,440
138
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
 

Related Threads on Solving inequalties

  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
6
Views
2K
S
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
10
Views
5K
  • Last Post
Replies
13
Views
2K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
11
Views
5K
S
  • Last Post
Replies
3
Views
1K
Top