Discussion: Organize all the equations in some kind of order.
Is this a function or an equation or both?
Equation. x + 3 = 10; only one solution. An equation is only one way to express a relationship.
Function. For F(x) there is only one solution (unique answer). A function is a relationship between two variables such that every value of the independent variable, within the domain of the function, maps to one value for the dependent variable.
Functions can pass a verticle line test (a visual way to determine if a curve is a graph of a function or not by seeing if the line passes through multiple y points above the same point on x. If it does, then there are more than one solution. For example, a graph in the shape of the letter S would have three points above one or more of the same x point.
Both Equation and Function. x = 2y + 3
Not all functions can be expressed in any familiar way as an equation, but all functions can be used to make equations.