Imaginary Part

The imaginary part $\Im$ of a Complex Number $z=x+iy$ is the Real Number multiplying i, so $\Im[x+iy]=y$. In terms of $z$ itself,

$$\Im[z]={z-z^*\over 2i},$$

where $z^*$ is the Complex Conjugate of $z$.

See also Absolute Square, Complex Conjugate, Real Part

References

Abramowitz, M. and Stegun, C. A. (Eds.). Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing. New York: Dover, p. 16, 1972.