A single-variable function is a function that contains only one variable.
For example, f(x)=2x is a single-variable function with the single variable being represented by x.
Note that y=2x is also a single-variable function because this is simply a different notation used for graphing the function (i.e. on the y axis). But in reality y=2x really means y=f(x)=2x . The y is just a placeholder for the function of x, f(x). It is not another variable that we set equal to a number as an input.
In other words, if we put in a value for x, and then run the function, we will get a result which is “The function f, of x. We then simply plot that result, x giving us the x-axis input and f(x) giving us the y-axis output. Therefore, any point on a graph is really just showing what output comes from each input.
In contrast to single-variable functions, multivariable functions contain two or more variables in the input and/or the output.