$\"\"$

\

Observe the figure :

\

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

\

$\"\"$

\

Consider the triangle

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$\"\"$

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Law of cosines : $\"\"$

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$\"\"$

\

$\"\"$

\

$\"\"$ .

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$\"\"$

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The length of $\"\"$ .

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From the figure, $\"\"$ is the mid point of $\"\"$ .

\

$\"\"$

\

Draw the right angle $\"\"$ from the figure.

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$\"\"$

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The lengths are $\"\"$ and $\"\"$ .

\

From Pythagorean Theorem:

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$\"\"$

\

$\"\"$

\

Observe the figure

\

$\"\"$

\

Therefore $\"\"$ .

\

Consider the triangle $\"\"$ shown below.

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$\"\"$

\

\

From the figure $\"\"$ and $\"\"$ .

\

From the properties of $\"\"$ ., $\"\"$ and $\"\"$ triangles, $\"\"$ .

\

Hence $\"\"$ .

\

$\"\"$

\

Consider the $\"\"$ shown below :

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$\"\"$

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From the total figure, $\"\"$ , $\"\"$ and $\"\"$ .

\

Consider $\"\"$ :

\

Law of cosines : $\"\"$

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$\"\"$

\

$\"\"$

\

$\"\"$ .

\

$\"\"$

\

$\"\"$ .