Complex number

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Numbers with two dimensions are called complex numbers, that you can write as

z = a + bi

and they consist of the real numbers a, b and the unit i.

i² = –1

You see it in the table

1 i

i −1

Complex numbers can be used to describe a rotation in two dimensions.

The Irisch mathematcian William Rowan Hamilton (1805 - 1865) worked on multi-dimensional numbers.