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.
Lawrence Hall of Science
The Math Page: Skill in Algebra: The Slope of a Straight Line
Here is a site that clearly and thoroughly explains many topics surrounding the slope of a line, including slope of horizontal, vertical, parallel, and perpendicular lines in addition to the formula and concept of slope. There are...
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.
CK-12 Foundation
Ck 12: Algebra: Determining the Equation of a Line
This comprehensive study guide highlights the main terms and formulas needed to determine the equation of a line. Examples are included.