A proportionality relationship happens when two quantities or numbers x and y are related multiplicatively by a fixed number. This can occur when either their ratio x/y is a fixed number (direct proportionality), or their product xy is a fixed number (inverse proportionality). If x is directly proportional to y, then we write \displaystyle{ x \propto y }. The fixed number of a proportionality relationship is called the constant of proportionality. view more...