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

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The given funtion is $\"\"$ and $\"\"$

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Compare the above two equations.

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We get,

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$\"\"$

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$\"\"$ (Add 21 to each side) \ \

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

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

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$\"\"$ (Add: $\"\"$ ) $\"\"$

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$\"\"$ (Multiply each side by negative one)

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$\"\"$ (Product of two same signs is positive)

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$\"\"$ (Divide each side by 2) \ \

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$\"\"$ (Cancel common terms) \ \ $\"\"$

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The value of $\"\"$ .

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