We also encountered a category of equations that contain two unknown variables. We saw equations that appeared in the basic form ax + by = c, and also saw how we could use the rules to modify, or transform them into the equivalent form y = -a/b x + c/b. The important fact that we learned from the 2-variable equations was that with two unknown values, it is possible to determine one value as an expression that depends on the other value. It is not possible, however, to explicitly determine both values without more information. While the equations do not enable us to determine both values unconditionally, they do however define a relation between the two unknown values.