variation

In mathematics, a practical relationship between two variables. Direct variation (when the values of the variables maintain a constant ratio) corresponds to y = kx on a straight line graph, for example distance travelled at a steady speed. Inverse variation (when an increase in the value of one variable results in a decrease in that of the other) corresponds to y =k/x on a rectangular hyperbolic graph, for example the price of an article and the quantity that can be bought for a fixed sum of money. In problems of direct and inverse variation, the first step is to find the value of k.