$\"\"$

The points are $\"\"$ .

Let the slope of the line be $\"\"$ .

Derive the slope $\"\"$ by using the formula $\"\"$ .

$\"\"$ (Substitute $\"\"$ )

$\"\"$ (Subtract: $\"\"$ ) $\"\"$

If the two nonvertical lines are parallel, then their slopes are equal. That is $\"\"$ .

Therefore slope of a parallel line $\"\"$ is also $\"\"$ .

If the two nonvertical lines are perpendicular, then their slopes are negative reciprocals of each other. That is $\"\"$ .

Therefore slope of perpendicular line is $\"\"$ .

$\"\"$

The slope of a parallel line is $\"\"$ and the slope of a perpendicular line is $\"\"$ .