2.σ: indicates summation, usually an indicator. The lower boundary value is written in its lower part and the upper boundary value is written in its upper part;

3, m: stands for a matrix or series or something else;

4.DF/DX:F's derivative about X is also the linear approximate slope of F;

5、A？ B×C: scalar triple product, determinant of a, b and c column matrix.

Extended data:

The invention and use of mathematical symbols are later than numbers, but their number exceeds numbers. There are more than 200 mathematical symbols commonly used in modern mathematics, and each symbol has an interesting experience.

For example, there used to be several kinds of plus signs, and the "+"sign is commonly used in modern mathematics. "+"comes from Lavin "et" (meaning "harmony"). /kloc-in the 6th century, Italian scientist Nicolo Tartaglia used the first letter of Italian word "plu" (meaning "add") to indicate addition, and the grass was "μ", which finally became "+".

The number "-"is derived from the Latin word "minus" (meaning "minus"). At first, it was abbreviated as m, but later it was simplified to "-"because of its fast writing.