12 Constant of VariationThe constant of variation is the steady rate of change. The constant k is the constant of variation, or the constant of proportionality.
13 Example 2Indicate which equations represent a direct variation. If an equation describes a direct variation, give the constant of variation.f(x) = 2.2xdirect variation; k = 2.2
14 y = 4x − 1This is not a direct variation; the variable must be a multiple of x.d = 45tThis is a direct variation; k = 45.y = −2xThis is not a direct variation; the coefficient of x must be positive.