What I Have Learned In this module, you have learned the following concepts about variation. 1. The four types of variation are direct, inverse, joint, and combined. 2. The letter k represents the constant of variation, 3. The statement, "y is proportional to x" is an example of direct variation. 4. "An increase in x causes a decrease in yº is an example of inverse variation. 5. Joint variation is the same as direct variation with two or more quantities. 6. The kind of variation that involves both the direct and inverse variations is a combined variation.​