## Precalculus (6th Edition) Blitzer

Variation formulas define the relation between two quantities such that if one quantity varies, we know how the other is affected. The equation provided is: $z=\frac{k\sqrt{x}}{{{y}^{2}}}$. The above equation is a case of combined variation. In combined variation, both types of direct and inverse variations occur at the same time. In this equation, as soon as the value of x increases, the value of z will also increase but as soon as value of y increases, the value of z will decrease. We also have k, which is a constant of variation that controls the degree/strength of the variation.