$\"\"$

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The equation is $\"\"$ .

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Divide each side by 3.

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$\"\"$

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$\"\"$

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$\"\"$

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Case:1 a = b.

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$\"\"$

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Multiply each side by 3.

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$\"\"$

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$\"\"$

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Apply distributive property: a( b + c) = ab + ac.

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$\"\"$

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$\"\"$

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Subtract 3a from each side.

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$\"\"$

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$\"\"$

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Subtract 21 from each side.

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$\"\"$

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$\"\"$

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Divide each side by 3.

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Case:2 a = $\"\"$ b.

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$\"\"$

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Multiply each side by 3.

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Apply distributive property: a( b + c) = ab + ac.

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$\"\"$

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$\"\"$

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Add 3a to each side.

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$\"\"$

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$\"\"$

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Subtract 21 from each side.

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$\"\"$

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$\"\"$

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Divide each side by 9.

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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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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$\"\"$

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$\"\"$

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The absolute value of 1 is 1.

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$\"\"$

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The equality is true. $\"\"$

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Check:

\

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

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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

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$\"\"$

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The equality is true. $\"\"$

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The solution set is $\"\"$ .

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