What is a relationship in which the ratio of two variable quantities is constant in math?

In mathematics, a relationship in which the ratio of two variable quantities is constant is known as a direct variation. This means that as one variable increases or decreases, the other variable changes in a proportional manner. It can be represented by the equation ( y = kx ), where ( k ) is a constant. For example, if ( k = 2 ), then for every increase of 1 in ( x ), ( y ) will increase by 2.