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Solution - Absolute value equations

Exact form: z=7
z=-7

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
|z+5|=|z+9|
without the absolute value bars:

|x|=|y||z+5|=|z+9|
x=+y(z+5)=(z+9)
x=y(z+5)=(z+9)
+x=y(z+5)=(z+9)
x=y(z+5)=(z+9)

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||z+5|=|z+9|
x=+y , +x=y(z+5)=(z+9)
x=y , x=y(z+5)=(z+9)

2. Solve the two equations for z

5 additional steps

(z+5)=(z+9)

Subtract from both sides:

(z+5)-z=(z+9)-z

Group like terms:

(z-z)+5=(z+9)-z

Simplify the arithmetic:

5=(z+9)-z

Group like terms:

5=(z-z)+9

Simplify the arithmetic:

5=9

The statement is false:

5=9

The equation is false so it has no solution.

12 additional steps

(z+5)=-(z+9)

Expand the parentheses:

(z+5)=-z-9

Add to both sides:

(z+5)+z=(-z-9)+z

Group like terms:

(z+z)+5=(-z-9)+z

Simplify the arithmetic:

2z+5=(-z-9)+z

Group like terms:

2z+5=(-z+z)-9

Simplify the arithmetic:

2z+5=9

Subtract from both sides:

(2z+5)-5=-9-5

Simplify the arithmetic:

2z=95

Simplify the arithmetic:

2z=14

Divide both sides by :

(2z)2=-142

Simplify the fraction:

z=-142

Find the greatest common factor of the numerator and denominator:

z=(-7·2)(1·2)

Factor out and cancel the greatest common factor:

z=7

3. Graph

Each line represents the function of one side of the equation:
y=|z+5|
y=|z+9|
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.