$\"\"$

\

The angle $\"\"$ .

\

Observe the figure, $\"\"$ .

\

The sum of the three angles in any triangle is $\"\"$ .

\

In $\"\"$ , $\"\"$ .

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$ .

\

$\"\"$

\

The value of $\"\"$ .