Final answer:
In mathematics, formulas are used to convey a specific meaning or perform a specific function. Free variables can be used to represent relationships in formulas. Whether something is considered 'use' or 'mention' depends on the context and the speaker's intent.
Step-by-step explanation:
In mathematics, when we use formulas, we are employing them to convey a particular meaning or perform a specific function. In the case of the formula 'x+1=2', it is being used to express the fact that, for a particular value of x (in this case, 1), the formula is true. This is an example of using the formula, as it is being employed to convey a specific meaning.
Free variables can be used in a similar way to other variables. For example, if we have a formula with a free variable x, we can use that formula to represent a relationship between x and other variables in the formula.
Whether something is considered 'use' or 'mention' depends on the context and the speaker's intent. If a statement like 'two is a prime number' is mentioned without expressing a personal opinion, it could be considered a mention. However, if the statement is used to make a point or express an opinion, it could be considered a use.