# Index

## Index

Small number to the lower right of the letter it characterizes and that is generally used to number it.

• It is important not to confuse the terms “index” and “exponent”, since “$$x_{2}$$” is read as “$$x$$ index 2″ and “$${x}^{2}$$” is read as “x exponent 2″.
• There is also the index of a radical; in the expression $$\sqrt[3]{27}$$, the number 3 is the index of the radical. When the radical does not have an index, as in $$\sqrt{27}$$, the index of the radical is understood to be 2.

### Notation

In the expression $$x_{1}$$, the number 1 is written as an index of the letter $$x$$ and is read “$$x$$ index 1″.