You may want to review imaginary numbers first.

You can add or subtract multiples of *i* with real numbers,
and then it's called a complex number. (Technically, the real and
imaginary numbers are also special kinds of complex number; so, if
you're asked, “Is this number complex?” the answer's
almost certain to be yes.) Suppose you're given the
equation *x* − 3*i* = 1 + *yi*. If you know
that *x* and *y* are both real numbers, then you know
what *x* and *y* are; *x* = 1 and *y* =
−3.