Absolute Value Inequality: How to Solve and Graph

I think you will find that if you sketch y = ([3/(x-1)] - 5) you will find that it is positive when x is in the range (1, 4) and negative when x is outside that range, and that y = |3/(x-1)] - 5 | is the reflection of that part of the graph that is above the x-axis. So if 1 < x < 4 what can you say about y?In summary, the first step is to simplify the inequality to -4 < 3/(x-1) - 5 < 4 by multiplying both sides by (x-1) and adding 5 to all three members. Then, because
  • #1
lovemake1
149
1

Homework Statement



l [3/(x-1)] - 5l < 4

Homework Equations


The Attempt at a Solution



My 1st step was to make the inequality like this. -4 < 3/(x-1) - 5 < 4
and then i multiplied (x-1) to both left and right side and as well as to the 5.
but in the end, my result turns out to be really wrong.
I got 9/5 < x < 4/5
which is not possible.

please help.
 
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  • #2
lovemake1 said:

Homework Statement



l [3/(x-1)] - 5l < 4


Homework Equations





The Attempt at a Solution



My 1st step was to make the inequality like this. -4 < 3/(x-1) - 5 < 4
and then i multiplied (x-1) to both left and right side and as well as to the 5.
Instead of multiplying first, add 5 to all three members. That will give you 3/(x - 1) in the middle of the inequality. Remember, you can always add any amount to both (or all) sides of an inequality.

You can multiply both (or all) members of an inequality by a positive number, without changing the direction of the inequality signs. If you multiply the members by a negative value, all of the inequality signs change direction. Remember that?

Since you don't know the sign of x - 1, you're going to have to look at two cases: one where x - 1 > 0, and the other where x - 1 < 0. Each case will give you a different inequality to solve.
lovemake1 said:
but in the end, my result turns out to be really wrong.
I got 9/5 < x < 4/5
which is not possible.

please help.
 
  • #3
even if i add 5 to both side, i still get a very weird inequality.

i'll show my steps so you can see where i went wrong

-1 < 3(x-1) < 9
-1(x-1) < 3 < 9(x-1)
-x + 1 < 3 < 9x -9
-2 < -8x < -12
2/8 > x > 12/8

12/8 < x < 2/8

where did i possibly go wrong? please help.
 
  • #4
lovemake1 said:
even if i add 5 to both side, i still get a very weird inequality.

i'll show my steps so you can see where i went wrong

-1 < 3(x-1) < 9
Here (above). -4 + 5 isn't -1.
lovemake1 said:
-1(x-1) < 3 < 9(x-1)
When you multiply by x - 1 you need to have two separate inequalities, as I explained earlier.
lovemake1 said:
-x + 1 < 3 < 9x -9
-2 < -8x < -12
2/8 > x > 12/8

12/8 < x < 2/8

where did i possibly go wrong? please help.
 
  • #5
Two separate inequalities..
do you mean from x-1 < 3 < 4x-4 into x-1 < 3 and 4x-4 < 3
solve seperately ?

using this method i got an answer that is reasonable.

x -1 < 3
x < 4

and

4x - 4 > 3
4x > 7
x > 7/4


so therefore, 7/4 < x < 4

Is this correct?
 
  • #6
I expect you will clear that up - the fact that you were able to recognise a wrong answer is a good thing. I just wanted to say I think you have to watch out

Edit: some nonsense deleted.


It is always going to be useful to you from now on to sketch the graph of the function. First sketch y = ([3/(x-1)] - 5). Then reflect everything that is in the negative (y < 0) part of the graph in the positive half. Then the whole graph that is in the positive (upper) part is y = |[3/(x-1)] - 5 | .

You will then see easily what I mean if I say the inequality is true in a finest range of x, whereas if you had 6 instead of 4 on the right of the inequality it would be true for two infinite ranges of x, and the sketching habit will save you no end of trouble and confusion from now on.
 
Last edited:

FAQ: Absolute Value Inequality: How to Solve and Graph

What is absolute value inequality?

Absolute value inequality is a type of mathematical inequality that involves the absolute value of a variable. It is used to express relationships between quantities that have both positive and negative values.

How do you solve absolute value inequalities?

To solve an absolute value inequality, you first isolate the absolute value expression on one side of the inequality sign. Then, you split the inequality into two cases, one for when the expression inside the absolute value is positive, and one for when it is negative. Finally, you solve each case separately and combine the solutions to get the final solution.

What is the difference between absolute value equations and inequalities?

The main difference between absolute value equations and inequalities is that equations have an equal sign (=) while inequalities have an inequality sign (≤ or ≥). In other words, equations express that two quantities are equal, while inequalities express that one quantity is less than or greater than another.

Why is absolute value important in real-world applications?

Absolute value is important in real-world applications because it allows us to represent and analyze quantities that can have both positive and negative values. This is particularly useful in situations where we need to measure distance, such as in physics or engineering problems.

Can absolute value inequalities have more than one solution?

Yes, absolute value inequalities can have more than one solution. In fact, there can be infinitely many solutions, depending on the complexity of the inequality. It is important to carefully check the solutions obtained and make sure they satisfy the original inequality.

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