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Solution - Absolute value equations

Exact form: x=3,3
x=-3 , -3

Other Ways to Solve

Absolute value equations

Step-by-step explanation

1. Rewrite the equation with one absolute value terms on each side

|2x+6|+|5x15|=0

Add |5x15| to both sides of the equation:

|2x+6|+|5x15||5x15|=|5x15|

Simplify the arithmetic

|2x+6|=|5x15|

2. Rewrite the equation without absolute value bars

Use the rules:
|x|=|y|x=±y and |x|=|y|±x=y
to write all four options of the equation
|2x+6|=|5x15|
without the absolute value bars:

|x|=|y||2x+6|=|5x15|
x=+y(2x+6)=(5x15)
x=y(2x+6)=(5x15)
+x=y(2x+6)=(5x15)
x=y(2x+6)=(5x15)

When simplified, equations x=+y and +x=y are the same and equations x=y and x=y are the same, so we end up with only 2 equations:

|x|=|y||2x+6|=|5x15|
x=+y , +x=y(2x+6)=(5x15)
x=y , x=y(2x+6)=(5x15)

3. Solve the two equations for x

14 additional steps

(2x+6)=-(-5x-15)

Expand the parentheses:

(2x+6)=5x+15

Subtract from both sides:

(2x+6)-5x=(5x+15)-5x

Group like terms:

(2x-5x)+6=(5x+15)-5x

Simplify the arithmetic:

-3x+6=(5x+15)-5x

Group like terms:

-3x+6=(5x-5x)+15

Simplify the arithmetic:

3x+6=15

Subtract from both sides:

(-3x+6)-6=15-6

Simplify the arithmetic:

3x=156

Simplify the arithmetic:

3x=9

Divide both sides by :

(-3x)-3=9-3

Cancel out the negatives:

3x3=9-3

Simplify the fraction:

x=9-3

Move the negative sign from the denominator to the numerator:

x=-93

Find the greatest common factor of the numerator and denominator:

x=(-3·3)(1·3)

Factor out and cancel the greatest common factor:

x=3

12 additional steps

(2x+6)=-(-(-5x-15))

NT_MSLUS_MAINSTEP_RESOLVE_DOUBLE_MINUS:

(2x+6)=-5x-15

Add to both sides:

(2x+6)+5x=(-5x-15)+5x

Group like terms:

(2x+5x)+6=(-5x-15)+5x

Simplify the arithmetic:

7x+6=(-5x-15)+5x

Group like terms:

7x+6=(-5x+5x)-15

Simplify the arithmetic:

7x+6=15

Subtract from both sides:

(7x+6)-6=-15-6

Simplify the arithmetic:

7x=156

Simplify the arithmetic:

7x=21

Divide both sides by :

(7x)7=-217

Simplify the fraction:

x=-217

Find the greatest common factor of the numerator and denominator:

x=(-3·7)(1·7)

Factor out and cancel the greatest common factor:

x=3

4. List the solutions

x=3,3
(2 solution(s))

5. Graph

Each line represents the function of one side of the equation:
y=|2x+6|
y=|5x15|
The equation is true where the two lines cross.

Why learn this

We encounter absolute values almost daily. For example: If you walk 3 miles to school, do you also walk minus 3 miles when you go back home? The answer is no because distances use absolute value. The absolute value of the distance between home and school is 3 miles, there or back.
In short, absolute values help us deal with concepts like distance, ranges of possible values, and deviation from a set value.