To expand on what anonymous said: the imaginary number is the square root of -1, this is because there is no possible "real" answer to it, but you can use the imaginary number to calculate things (often used in engineering).
i=√−1
Sometimes you might come across something with a negative surd. To show this in terms of "i", just seperate the square root of -1 from the rest of the surd.
Example:
Let's so I want 7*square-root(-16 * 9):
7×√(−16)×9
7×√−25
7×√25×√−1
7×5×i
35i
To expand on what anonymous said: the imaginary number is the square root of -1, this is because there is no possible "real" answer to it, but you can use the imaginary number to calculate things (often used in engineering).
i=√−1
Sometimes you might come across something with a negative surd. To show this in terms of "i", just seperate the square root of -1 from the rest of the surd.
Example:
Let's so I want 7*square-root(-16 * 9):
7×√(−16)×9
7×√−25
7×√25×√−1
7×5×i
35i