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Solution - Absolute value equations

Exact form: y=-916,-1532
y=-\frac{9}{16} , -\frac{15}{32}
Decimal form: y=0.562,0.469
y=-0.562 , -0.469

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+12|=|13y+18|
without the absolute value bars:

|x|=|y||y+12|=|13y+18|
x=+y(y+12)=(13y+18)
x=-y(y+12)=-(13y+18)
+x=y(y+12)=(13y+18)
-x=y-(y+12)=(13y+18)

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+12|=|13y+18|
x=+y , +x=y(y+12)=(13y+18)
x=-y , -x=y(y+12)=-(13y+18)

2. Solve the two equations for y

27 additional steps

(y+12)=(13y+18)

Subtract from both sides:

(y+12)-13·y=(13y+18)-13y

Group like terms:

(y+-13·y)+12=(13·y+18)-13y

Group the coefficients:

(1+-13)y+12=(13·y+18)-13y

Convert the integer into a fraction:

(33+-13)y+12=(13·y+18)-13y

Combine the fractions:

(3-1)3·y+12=(13·y+18)-13y

Combine the numerators:

23·y+12=(13·y+18)-13y

Group like terms:

23·y+12=(13·y+-13y)+18

Combine the fractions:

23·y+12=(1-1)3y+18

Combine the numerators:

23·y+12=03y+18

Reduce the zero numerator:

23y+12=0y+18

Simplify the arithmetic:

23y+12=18

Subtract from both sides:

(23y+12)-12=(18)-12

Combine the fractions:

23y+(1-1)2=(18)-12

Combine the numerators:

23y+02=(18)-12

Reduce the zero numerator:

23y+0=(18)-12

Simplify the arithmetic:

23y=(18)-12

Find the lowest common denominator:

23y=18+(-1·4)(2·4)

Multiply the denominators:

23y=18+(-1·4)8

Multiply the numerators:

23y=18+-48

Combine the fractions:

23y=(1-4)8

Combine the numerators:

23y=-38

Multiply both sides by inverse fraction :

(23y)·32=(-38)·32

Group like terms:

(23·32)y=(-38)·32

Multiply the coefficients:

(2·3)(3·2)y=(-38)·32

Simplify the fraction:

y=(-38)·32

Multiply the fraction(s):

y=(-3·3)(8·2)

Simplify the arithmetic:

y=-9(8·2)

y=-916

28 additional steps

(y+12)=-(13y+18)

Expand the parentheses:

(y+12)=-13y+-18

Add to both sides:

(y+12)+13·y=(-13y+-18)+13y

Group like terms:

(y+13·y)+12=(-13·y+-18)+13y

Group the coefficients:

(1+13)y+12=(-13·y+-18)+13y

Convert the integer into a fraction:

(33+13)y+12=(-13·y+-18)+13y

Combine the fractions:

(3+1)3·y+12=(-13·y+-18)+13y

Combine the numerators:

43·y+12=(-13·y+-18)+13y

Group like terms:

43·y+12=(-13·y+13y)+-18

Combine the fractions:

43·y+12=(-1+1)3y+-18

Combine the numerators:

43·y+12=03y+-18

Reduce the zero numerator:

43y+12=0y+-18

Simplify the arithmetic:

43y+12=-18

Subtract from both sides:

(43y+12)-12=(-18)-12

Combine the fractions:

43y+(1-1)2=(-18)-12

Combine the numerators:

43y+02=(-18)-12

Reduce the zero numerator:

43y+0=(-18)-12

Simplify the arithmetic:

43y=(-18)-12

Find the lowest common denominator:

43y=-18+(-1·4)(2·4)

Multiply the denominators:

43y=-18+(-1·4)8

Multiply the numerators:

43y=-18+-48

Combine the fractions:

43y=(-1-4)8

Combine the numerators:

43y=-58

Multiply both sides by inverse fraction :

(43y)·34=(-58)·34

Group like terms:

(43·34)y=(-58)·34

Multiply the coefficients:

(4·3)(3·4)y=(-58)·34

Simplify the fraction:

y=(-58)·34

Multiply the fraction(s):

y=(-5·3)(8·4)

Simplify the arithmetic:

y=-15(8·4)

y=-1532

3. List the solutions

y=-916,-1532
(2 solution(s))

4. Graph

Each line represents the function of one side of the equation:
y=|y+12|
y=|13y+18|
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.