Imaginary unit

Principal square root of minus 1

The imaginary unit, usually denoted by i, is a mathematical constant that is a solution to the quadratic equation x2 = −1, which is not solved by any real number. Any real-number multiple of the imaginary unit is called an imaginary number. By combining the real numbers with the imaginary unit using addition and multiplication, a new number system known as the complex numbers is formed; it consists of all numbers of the form a + bi with real numbers a and b.

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