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Solution - Absolute value equations

Exact form: z=14
z=\frac{1}{4}
Decimal form: z=0.25
z=0.25

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+38|=|z-78|
without the absolute value bars:

|x|=|y||z+38|=|z-78|
x=+y(z+38)=(z-78)
x=-y(z+38)=-(z-78)
+x=y(z+38)=(z-78)
-x=y-(z+38)=(z-78)

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+38|=|z-78|
x=+y , +x=y(z+38)=(z-78)
x=-y , -x=y(z+38)=-(z-78)

2. Solve the two equations for z

5 additional steps

(z+38)=(z+-78)

Subtract from both sides:

(z+38)-z=(z+-78)-z

Group like terms:

(z-z)+38=(z+-78)-z

Simplify the arithmetic:

38=(z+-78)-z

Group like terms:

38=(z-z)+-78

Simplify the arithmetic:

38=-78

The statement is false:

38=-78

The equation is false so it has no solution.

18 additional steps

(z+38)=-(z+-78)

Expand the parentheses:

(z+38)=-z+78

Add to both sides:

(z+38)+z=(-z+78)+z

Group like terms:

(z+z)+38=(-z+78)+z

Simplify the arithmetic:

2z+38=(-z+78)+z

Group like terms:

2z+38=(-z+z)+78

Simplify the arithmetic:

2z+38=78

Subtract from both sides:

(2z+38)-38=(78)-38

Combine the fractions:

2z+(3-3)8=(78)-38

Combine the numerators:

2z+08=(78)-38

Reduce the zero numerator:

2z+0=(78)-38

Simplify the arithmetic:

2z=(78)-38

Combine the fractions:

2z=(7-3)8

Combine the numerators:

2z=48

Find the greatest common factor of the numerator and denominator:

2z=(1·4)(2·4)

Factor out and cancel the greatest common factor:

2z=12

Divide both sides by :

(2z)2=(12)2

Simplify the fraction:

z=(12)2

Simplify the arithmetic:

z=1(2·2)

z=14

3. Graph

Each line represents the function of one side of the equation:
y=|z+38|
y=|z-78|
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.