The general equation or standard equation of a straight line is given by

Where and are any constants and also either or .

__CASE – I__**: **If or , then the general equation or standard equation of straight line can be written of the form

Which is the equation of straight line parallel to -axis. Thus, the line is parallel to -axis if .

__CASE – II__**: **If or , then the general equation or standard equation of straight line can be written of the form

Which is the equation of straight line parallel to -axis. Thus, the line is parallel to -axis if .

__CASE – III__**: **If or , then the general equation or standard equation of straight line can be written of the form

Which is the equation of straight line in slope intercept form with slope is and -intercept is .