Direct variation can be expressed as an equation, an algebraic expression or a geometric expression. To illustrate the concept of direct variation as an equation, take the equation y/x = 6. Y varies directly with X, with 6 being the constant in the equation. From the equation, it can be determined that Y is always six times greater than X. The equation y = kx is an example of an algebraic equation that illustrates direct variation. Both Y and X are always multiplied by the same amount. This equation is a linear equation. In addition to direct variations, other relationships between numbers and variables that remain constant exist in the mathematical world. Variables A and B are said to be inversely related to each other when A varies as the reciprocal of B. Variables can also be jointly related.