$\"\"$

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Consider the $\"\"$ .

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The sides are $\"\"$ , $\"\"$ and $\"\"$ .

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Pythagorean Theorem : $\"\"$ .

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$\"\"$

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$\"\"$

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From the $\"\"$ ,

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

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$\"\"$

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Substitute $\"\"$ and $\"\"$ in $\"\"$ .

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$\"\"$

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Therefore, the law of cosines : $\"\"$ .

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$\"\"$

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(b)

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Similarily solve $\"\"$ , and $\"\"$ by drawing the altitudes from and $\"\"$ and $\"\"$ .

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$\"\"$

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(a) The law of cosines : $\"\"$ .

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(b) Similarily solve $\"\"$ , and $\"\"$ by drawing the altitudes from and $\"\"$ and $\"\"$ .