This CoolMath Resource will help students determine if lines are perpendicular by finding the slope, using the point-slope formula, and graphing.

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...

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.