$\"\"$

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The side of triangle is $\"\"$ .

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The angle is $\"\"$

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$\"\"$

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Observe the diagram:

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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Consider $\"\"$ .

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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 sum of angles in a triangle is $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$

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$\"\"$ , $\"\"$ and $\"\"$ .