<P> In calculus and related areas of mathematics, a linear function from the real numbers to the real numbers is a function whose graph (in Cartesian coordinates with uniform scales) is a line in the plane . Their characteristic property that when the value of the input variable is changed, the change in the output is a constant multiple of the change in the input variable . </P> <P> Linear functions are related to linear equations . </P> <P> A linear function is a polynomial function in which the variable x has degree at most one, which means it is of the form </P> <Dl> <Dd> f (x) = ax + b . </Dd> </Dl>

If y is a linear function of x then