$\"\"$

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Prove that: $\"\"$ .

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Consider $\"\"$ .

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$\"\"$

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$\"\"$

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Substitute area formula: $\"\"$ .

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$\"\"$

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$\"\"$

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Similarly $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Substitute formula: $\"\"$ .

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$\"\"$

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Substitute area formula: $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$

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The expression $\"\"$ is proved.