An imaginary number is the square root of a negative real number. (The square root of a number is a second number that, when multiplied by itself, equals the first number.) As an example, √−25 is an imaginary number.

The problem with imaginary numbers arises because the square (the result of a number multiplied by itself) of any real number is always a positive number. For example, the square of 5 is 25. But the square of −5 (−5 × −5) is also 25. What does it mean, then, to say that the square of some number is −25. In other words, what is the answer to the problem √−25 = ?

As early as the sixteenth century, mathematicians were puzzled by this
question. Italian mathematician Girolamo Cardano (1501–1576) is
generally regarded as the first person to have studied imaginary numbers.
Eventually, a custom developed for using the lowercase letter
*
i
*
to represent the square root of a negative number. Thus √−1
=
*
i
*
, and √−25 = √25 × √−1 = 5
*
i
*
.

Imaginary numbers were largely a stepchild in mathematics until the
nineteenth century. Then, they were incorporated into another mathematical
concept known as complex numbers. A complex number is a number that
consists of a real part and an imaginary part. For example, the number 5 +
3
*
i
*
is a complex number because it contains a real number (5) and an
imaginary number (3
*
i
*
). One reason complex numbers are important is that they can be
manipulated in ways so as to eliminate the imaginary part.

[
*
See also
*
**
Complex numbers
**
]

Also read article about **Imaginary Number** from Wikipedia

1

hi

Dec 7, 2009 @ 4:16 pm

Who actually developed and came up with imaginary numbers? Please give one specific name if possible.