$\"\"$

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Find remaining parts.

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

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Apply cosine law : $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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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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$\"\"$

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$\"\"$

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$\"\"$

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In a triangle the sum of the three angles 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 $\"\"$ .