$\"\"$

Consider $\"\"$ .

Law of sines: $\"\"$ .

$\"\"$

$\"\"$ is the altitude from a vertex to the opposite side $\"\"$ .

$\"\"$

Substitute $\"\"$ .

$\"\"$

The altitude from a vertex to the opposite side $\"\"$ is $\"\"$ .

$\"\"$

The altitude from a vertex to the opposite side $\"\"$ is $\"\"$ .