Question 1012267
.
{{{P[1]}}}=( p, a ); {{{P[2]}}}=( p, - a )
.
1. {{{slope=(y[2]-y[1])/(x[2]-x[1])}}}={{{(-a-a)/(p-p)}}}
Division by zero (p-p=0) is undefined. 
Vertical lines have undefined slope.
The line is vertical.
.
2. Equation: Vertical lines have equation of form x=n
In this case, the x value is p
Equation: x=p
.
3. Since p cannot be zero, there is no y-intercept.
x value must be zero to cross y axis.
(The line is parallel to the y axis)
.
4. Line perpendicular to vertical line is horizontal.
Horizontal lines have slope m=0.