How can constraints be used to model a real-world situation?

It is possible that certain solutions which make an equation true mathematically, may not make any sense in the context of a real-world word problem. Constraints then become necessary to allow the mathematical model to realistically represent the situation.

It is possible to set constraints on the x-values (the independent variable)
or the y-values (dependent variable) associated with an equation.

When graphing, the set of all possiblex-coordinates used to create the graph are referred to as the domain. Constraints may already be stated in a problem as limitations upon the domain, or may need to be specified if the situation is reality based.
The set of all of the y-coordinates used by the domain elements is called the range.

Sis less than or equal to 75 (bottom left)