Important points about slope

Lesson#3
Important points about slope
Points to remember:
If line is horizontal or parallel to x-axis or perpendicular to y-axis we say that a=0deg then ...
USE OF THE CONCEPT OF SLOPE AND ITS FORMULA:
To check the relation between two lines whether they are parallel or perpendicular to each other.
To check that triangle is right or not.
To check type of quadrilateral.
To check that the given points are collinear or not.
To write the equation of a straight line.
Many other applications
Introduction to Analytical Geometry
Chapter No 4
Exercise No 4.3
Mathematics
part 2