When the quotient of two variables is equal to a constant, they are said to have direct variation, or
direct proportionality. Algebraically, this relationship is represented as the constant being equal to the ratio of to
A joint variation, also known as joint proportionality, occurs when one variable depends on two or more variables and varies directly with each of them when the others are kept constant.
The variable has joint variation with and
A combined variation, or combined proportionality, is when one variable depends on two or more variables either directly, inversely, or a combination of both.
The variable depends on two other variables, and Therefore, this is a combined variation. Any joint variation is also a combined variation.