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Solution - Absolute value equations

Exact form: y=7,7
y=7 , 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
|y+7|=|y7|
without the absolute value bars:

|x|=|y||y+7|=|y7|
x=+y(y+7)=(y7)
x=y(y+7)=(y7)
+x=y(y+7)=(y7)
x=y(y+7)=(y7)

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||y+7|=|y7|
x=+y , +x=y(y+7)=(y7)
x=y , x=y(y+7)=(y7)

2. Solve the two equations for y

13 additional steps

(-y+7)=(y-7)

Subtract from both sides:

(-y+7)-y=(y-7)-y

Group like terms:

(-y-y)+7=(y-7)-y

Simplify the arithmetic:

-2y+7=(y-7)-y

Group like terms:

-2y+7=(y-y)-7

Simplify the arithmetic:

2y+7=7

Subtract from both sides:

(-2y+7)-7=-7-7

Simplify the arithmetic:

2y=77

Simplify the arithmetic:

2y=14

Divide both sides by :

(-2y)-2=-14-2

Cancel out the negatives:

2y2=-14-2

Simplify the fraction:

y=-14-2

Cancel out the negatives:

y=142

Find the greatest common factor of the numerator and denominator:

y=(7·2)(1·2)

Factor out and cancel the greatest common factor:

y=7

5 additional steps

(-y+7)=-(y-7)

Expand the parentheses:

(-y+7)=-y+7

Add to both sides:

(-y+7)+y=(-y+7)+y

Group like terms:

(-y+y)+7=(-y+7)+y

Simplify the arithmetic:

7=(-y+7)+y

Group like terms:

7=(-y+y)+7

Simplify the arithmetic:

7=7

3. List the solutions

y=7,7
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
y=|y+7|
y=|y7|
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.