A line passes through the points \( ( p , a ) \) and \( ( p , - a ) \) where \( p \) and \( a \) are real numbers and \( p \neq 0 . \) Describe each of the following. Explain your reasoning.
\( 1 \) slope of the line 2. equation of the line 3. yntntercept 4. slope of a line perpendicular to the given line