Khan Academy
Khan Academy: Algebra: Perpendicular Lines
This video demonstrates how to determine if lines are perpendicular given the equations. There are three equations listed but they are not all in slope-intercept form. Practice problems available. [3:29]
Khan Academy
Khan Academy: Algebra: Perpendicular Lines 2
This video demonstrates how to find the equation of a line when given a point on the line and the equation of a line perpendicular to it. Practice problems available. [3:01]