Purple Math
Purplemath: Straight Line Equations: Slope Intercept Form
Slope-intercept form of a line is shown in formulas and examples with this Purplemath lesson. There are examples of slope-intercept with the slope and a point and with two points. Includes interactive widgets for exploring concepts.
Cool Math
Coolmath: Perpendicular Lines
This CoolMath Resource will help students determine if lines are perpendicular by finding the slope, using the point-slope formula, and graphing.