$\"\"$

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Observe the figure, it is contain one big square and one small square.

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The length of the side of the big square is $\"\"$ .

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The area of the big square is $\"\"$ .

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$\"\"$

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Apply square of sum formula: $\"\"$ .

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$\"\"$ . $\"\"$

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The length of the side of the small square is $\"\"$ .

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The area of the big square is $\"\"$ .

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$\"\"$

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Apply square of a difference formula: $\"\"$ .

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$\"\"$ . $\"\"$

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The area of shaded region is $\"\"$ .

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$\"\"$

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$\"\"$

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Group like terms.

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$\"\"$

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combine like terms.

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$\"\"$

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$\"\"$

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The area of shaded region is $\"\"$ .