Direct variation is the relationship between two variables such that the variables have a constant ratio, k, where k is not equal to 0.
K is called the constant of variation.
Suppose that are variables are x and y and y varies directly with x. We can say that the ratio of y to x is equal to k where k is not equal to 0.
We can also rewrite this formula as y = kx where k is not equal to 0.
It's important to understand that we can use these two ratios interchangeably depending on what we're solving for in the problem.