$\"\"$ \ \

\

The eccentricity of a conic is $\"\"$ .

\

The eccentricity is $\"\"$ .

\

Observe the diagram:

\

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

\

$\"\"$

\

$\"\"$

\

Substitute $\"\"$ .

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$ .

\

$\"\"$

\

$\"\"$ . \ \