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Solution - Absolute value equations

Exact form: x=-4,-52
x=-4 , -\frac{5}{2}
Mixed number form: x=-4,-212
x=-4 , -2\frac{1}{2}
Decimal form: x=4,2.5
x=-4 , -2.5

Other Ways to Solve

Absolute value equations

Step-by-step explanation

1. 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
|x+1|=3|x+3|
without the absolute value bars:

|x|=|y||x+1|=3|x+3|
x=+y(x+1)=3(x+3)
x=y(x+1)=3((x+3))
+x=y(x+1)=3(x+3)
x=y(x+1)=3(x+3)

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||x+1|=3|x+3|
x=+y , +x=y(x+1)=3(x+3)
x=y , x=y(x+1)=3((x+3))

2. Solve the two equations for x

15 additional steps

(x+1)=3·(x+3)

Expand the parentheses:

(x+1)=3x+3·3

Simplify the arithmetic:

(x+1)=3x+9

Subtract from both sides:

(x+1)-3x=(3x+9)-3x

Group like terms:

(x-3x)+1=(3x+9)-3x

Simplify the arithmetic:

-2x+1=(3x+9)-3x

Group like terms:

-2x+1=(3x-3x)+9

Simplify the arithmetic:

2x+1=9

Subtract from both sides:

(-2x+1)-1=9-1

Simplify the arithmetic:

2x=91

Simplify the arithmetic:

2x=8

Divide both sides by :

(-2x)-2=8-2

Cancel out the negatives:

2x2=8-2

Simplify the fraction:

x=8-2

Move the negative sign from the denominator to the numerator:

x=-82

Find the greatest common factor of the numerator and denominator:

x=(-4·2)(1·2)

Factor out and cancel the greatest common factor:

x=4

16 additional steps

(x+1)=3·(-(x+3))

Expand the parentheses:

(x+1)=3·(-x-3)

(x+1)=3·-x+3·-3

Group like terms:

(x+1)=(3·-1)x+3·-3

Multiply the coefficients:

(x+1)=-3x+3·-3

Simplify the arithmetic:

(x+1)=-3x-9

Add to both sides:

(x+1)+3x=(-3x-9)+3x

Group like terms:

(x+3x)+1=(-3x-9)+3x

Simplify the arithmetic:

4x+1=(-3x-9)+3x

Group like terms:

4x+1=(-3x+3x)-9

Simplify the arithmetic:

4x+1=9

Subtract from both sides:

(4x+1)-1=-9-1

Simplify the arithmetic:

4x=91

Simplify the arithmetic:

4x=10

Divide both sides by :

(4x)4=-104

Simplify the fraction:

x=-104

Find the greatest common factor of the numerator and denominator:

x=(-5·2)(2·2)

Factor out and cancel the greatest common factor:

x=-52

3. List the solutions

x=-4,-52
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
y=|x+1|
y=3|x+3|
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.