1. Handwriting: letters, symbols and special symbols used to represent handwriting in mathematical formulas. Handwritten fonts simulate the style of handwriting, such as ""in English and ""in Greek letters.

2. Blackboard: used to represent special symbols such as vectors, matrices and sets in mathematical formulas. Bold characters on the blackboard are used to highlight important mathematical objects, such as "?" In English. Represents a set of real numbers.

3. Italic: used to represent variables or parameters in mathematical formulas. Italic fonts are used to distinguish mathematical symbols from ordinary text, such as "X" in English for variables.