If absolute value of a real number represents its distance from the origin on the number line then absolute value inequalities are type of inequalities that are consisted of absolute values.
If we are trying to solve a simple absolute value equation, the solution is quite simple, it usually has two solutions. For example 1.:
By solving any inequality we’ll get a set of solutions as our final solution, which means that this will apply to absolute inequalities as well.
Let’s try to solve example 1. but change the equality sign.
How would we put this task into words? If absolute value represents numbers distance from the origin, this would mean that we are searching for all numbers whose distance from the origin is lesser than two.
Instinctively we know that the solution for this inequality is the set , but how can we be sure?
First you break down your inequality into two parts: first is the part in which your expression in absolute value is positive, and second in which that expression is negative.
1. x ≥ 0 – if x is greater or equal to zero, we can just ignore absolute value sign and continue like it isn’t there. We got the inequality .
The solution for this inequality is . (Zero comes from our starting condition where x has to be greater than zero)
2. x < 0 – if x is lesser than zero, we have to change its sign. We got inequality . When we solve this simple inequality we get .
The solution for this inequality is . (Zero comes from our starting condition where x has to be lesser than zero)
Our final solution will be the union of these two intervals, which means that the final solution is in the form:
Note: You can also read this solution as: the solution is all x-es from the interval .
If we want to draw it on the number line:
Usually you’ll get a whole expression in your inequality. This is solved just like the example 2. Set your grounds first before going any further. Example2 is the basic absolute value inequality task, but using it you can solve any other absolute value task, no matter how complicated.
Again, we’ll divide it into two parts.
1. (x ≥ – 2) => => x ≥ – 1. The common solution for these two inequalities is the interval . (note that in these separate cases you are looking for the intersection between two intervals, but in the end you take the union of the pairs of intersected intervals).
2. (x < – 2) => => => x ≤ – 3. The common solution for these two inequalities is the interval .
The final solution is the union of solutions of separate parts:
First thing we have to do is find points where the absolute values will change terms inside of them.
We have two equations and whose zeros are -3 and 1.
Let’s draw them on a number line.
Those two points divide our number line onto three intervals. Our job not is to observe how these two absolute values act on each of the segments.
First interval is . We can insert any number from that interval into those two absolute values to see are they positive or negative. If they are positive, we leave them as they are, and if they are negative we change signs of all members of expressions in absolute values. You can insert any number, so we’ll use .
For the first absolute value => which is lesser than zero. This means that for the first interval first absolute value will change signs of its terms.
For the second absolute value => which is lesser than zero. This means that for the first interval second absolute value will change signs of its terms.
For the first absolute value => which is greater than zero. This means that for the second interval the first absolute value will not change signs of its terms.
For the second absolute value => which is lesser than zero. This means that for the second interval second absolute value will change signs of its terms.
For both absolute values the solution will be positive, which means that we leave them as they are.
The final solution is the union of these intervals which is, in this case, the whole set of real numbers.
Absolute value inequalities worksheets
Integers - One or less operations (541.1 KiB, 202 hits)
Integers - More than one operations (656.8 KiB, 216 hits)
Decimals - One or less operations (566.3 KiB, 197 hits)
Decimals - More than one operations (883.6 KiB, 188 hits)
Fractions - One or less operations (585.2 KiB, 196 hits)
Fractions - More than one operations (1,009.1 KiB, 195 hits)