Description: Learn how to write a proportional equation y=kx where k is the so-called "constant of proportionality". And remember, in order for it to be a proportional relationship, the ratio between the two variables is always constant. And so, you can actually use this information, the ratio, the ratio between y and x is this constant four, to express the relationship between y and x as an equation. In fact, in some ways this is, or in a lot of ways, this is already an equation, but I can make it a little bit clearer, if I multiply both sides by x.*Teacher Advisor is 100% free.