*i*

*i* is the symbol used to denote the principal square root of -1, also called the imaginary unit.

I is a high school-level concept that would be first encountered in a pre-calculus course covering complex numbers. It is listed in the California State Standards for Algebra II.

### Prerequisites

Imaginary Number: | In mathematics, an imaginary number is multiple of the imaginary unit i (the square root of -1). |

Root: | For a mathematical function, a root is a set of arguments for which the function assumes the value of zero. |

Square Root: | A square root of x is a number r such that r*r = x. |