\"\"\"\"

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The equation is \"\".

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Write two cases:

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Case-1: a = b.

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\"\"

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Case-2: a = -b

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\"\"

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\"\"

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Solve the equation for Case-1.

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\"\"

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According to subtraction property of equality: if \"\", then \"\".

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\"\"      (Subtract 9 from each side)

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\"\"                  (Apply Additive inverse property: \"\")

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\"\"                       (Subtract: \"\") \"\"

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Check:

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To check the solution, substitute \"\" in original equation.

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\"\"

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|21| = 21                 (Add: 12 + 9 = 21)

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The absolute value of 21 is 21.

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21 = 21

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Compare the values the equation is true. \"\" is a solution.\"\"

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Solve the equation for Case-2.

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\"\"

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According to addition property of equality: if a = b, then a + c = b + c.

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\"\"        (Subtract 9 from each side)

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\"\"                   (Apply Additive inverse property: \"\")

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\"\"                         (Subtract: \"\")\"\"

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Check:

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To check the solution, substitute \"\" in original equation.

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\"\"

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\"\"                    (Add: \"\")

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\"\"                          (The absolute value of \"\")

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Compare the values the equation is true. \"\" is a solution.\"\"

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The solutions are 12 and -30. The solution set is \"\".