Complex conjugate

In mathematics, the complex conjugate of a complex number is the number with equal real part and imaginary part equal in magnitude but opposite in sign. For example, the complex conjugate of 3 + 4i is 3 − 4i.

In polar form, the conjugate of ${\displaystyle \rho e^{i\phi }}$ is ${\displaystyle \rho e^{-i\phi }}$. This can be shown using Euler's formula.

Complex conjugates are important for finding roots of polynomials. According to the complex conjugate root theorem, if a complex number is a root to a polynomial in one variable with real coefficients (such as the quadratic equation or the cubic equation), so is its conjugate.

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