Then you can figure out which is the independent variable and which is the dependent variable: (Independent variable) causes a change in (Dependent Variable) and it isn't possible that (Dependent Variable) could cause a change in (Independent Variable). For example: (Time Spent Studying) causes a change in (Test Score) and it isn't possible that (Test Score) could cause a change in (Time Spent Studying).
Domain and Range. When we look at a function like f(x) = x + 2, we can easily say where the function f(x), in this case, the value along the y-axis, is at any point we choose along the x-axis. We know that at x = 3.4, f(x) = 5.4. The values of x that the function will output a value for is called the domain of f. In the case of f(x) = x + 2, the domain is the entire x-axis, or, formally speaking, all real numbers. The values which f(x) takes on is called the range of f.
Once I have x =, I'll switch x and y; the y = is the inverse. If you need to find the domain and range, look at the original function and its graph. The domain of the original function is the set of all allowable x-values; in this case, the function was a simple polynomial, so the domain was all real numbers.