$\"\"$ $\"\"$

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The expression is $\"\"$

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Apply subtraction property of equality; if $\"\"$ then $\"\"$ .

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$\"\"$ (Subtract 72 from each side)

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

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$\"\"$ (Additive identity property: $\"\"$ ) $\"\"$ $\"\"$ (Divide each side by 6)

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$\"\"$ (Cancel common terms)

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$\"\"$ (Divide: $\"\"$ )

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$\"\"$ (Take square root each side) $\"\"$ $\"\"$

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Product property of square roots:

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For nonnegative real numbers a and b, $\"\"$

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$\"\"$ $\"\"$

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Rewrite the ( $\"\"$ ) using imaginary unit; that is $\"\"$ where $\"\"$ .

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$\"\"$

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$\"\"$ (Find the square root: $\"\"$ )

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$\"\"$ (Multiply: $\"\"$ ) $\"\"$

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The value of $\"\"$ .