In this paper, variables can be expressed by formulas, and formulas can express the relationship between variables more clearly. Using formulas can also make it easier for readers to understand and repeat experiments. However, if the relationship between variables is simple or the formula is too complicated, the relationship between variables can be expressed in words.

When using formulas, you need to pay attention to the format and typesetting of formulas. Formulas should be written on a separate line and use standard mathematical symbols and typesetting rules. If the formula is long, you can write it line by line, and use appropriate brackets or symbols at the beginning of each line.

In addition to formulas, you can also express the relationship between variables in charts and other ways. Charts can express the relationship between variables more intuitively and make it easier for readers to understand.

In short, the representation of variables should be chosen according to the specific situation, and should be clear and concise.