## Trigonometry (10th Edition)

$\sqrt (-36)=\sqrt (-1\times36)=\sqrt -1 \times \sqrt (36)=i\times6=6i$ If a and b are real numbers, then any number of the form $a+bi$ is a complex number. Since $a=0$ and $b=6$ and both $a$ and $b$ are real numbers, $6i$ is a complex number. Also, If $a=0$ and $b\ne0$, the complex number is said to be a pure imaginary number. Since $b=6$, $6i$ can be labelled as a pure imaginary number as well. Since pure imaginary numbers are a subset of non-real complex numbers, $6i$ can be labelled as a non-real complex number as well.