Wolfram Research
Wolfram Math World: Direct Proportion
MathWorld offers a concise mathematical definition of direct variation or direct proportion.
Math Planet
Math Planet: Algebra 2: Rational Expressions: Variation
Provides an explanation and examples of variation.
Free Math Help
Free Math Help: Direct Variation
The discussion examines direct variation. Students learn about the math concept through definitions and sample exercises.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Combined Variation
Find a quick, concise explanation of Combined Variation. Hyperlinks are available to explain how variables can vary directly and inversely.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Direct Variation
Find a quick, concise explanation of what a direct variation is. An example is given and clearly explained.
University of Illinois
University of Illinois: Quadratic Formula
This site from the University of Illinois offers an excellent simulation of the quadratic formula, where you can type in different values for a, b, and c, and then view the change in the answer for x.
Oswego City School District
Regents Exam Prep Center: Practice With Direct Variation
This site has eleven interactive problems dealing with Direct Variation. Allows you to answer in multiple choice format and gives an explanation for the correct answer.
Purple Math
Purplemath: Variation Equations
Purplemath offers an extensive explanation of direct and inverse variation, containing several examples and real-world applications.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: High School Basic Algebra Review
An overview of basic high school algebra topics can be found here. Absolute value, signed numbers, inequalities and equations, mixture problems, and direct and indirect variation are all listed, each with links to questions posed by...