Proportionality (mathematics)
![Variable y is directly proportional to the variable x.](/Images/godic/202501/05/Proportional_variables.svg0830.png")
![Inverse proportionality with a function of y = 1/x.](/Images/godic/202501/05/Inverse_proportionality_function_plot0830.gif")
In mathematics, two variables are proportional if a change in one is always accompanied by a change in the other, and if the changes are always related by use of a constant multiplier. The constant is called the coefficient of proportionality or proportionality constant.