## Precalculus (6th Edition)

RECALL: The complex number $a+bi$ is: (i) a pure imaginary number when $a=0$ and $b\ne0$; (ii) a real number when $b=0$; (iii) a nonreal complex number when $b\ne0$. The given expression $-7i$ has $a=0$. Thus, it is a: pure imaginary number; nonreal complex number; and complex number