**Complex Numbers**

The
standard form for a complex number is *a*** + ***b**i*,
where *i* is the imaginary unit, .
You do complex arithmetic (addition, subtraction, multiplication, division, and
exponentiation) the same way as you do real number arithmetic. The imaginary unit,
*i*, is located above the 0 key. Accordingly, press **SHIFT**
*i* to enter *i*. The screen
at right shows the familiar equation *i*^{2} = -1 obtained in the
RUN-MAT screen.

Complex number arithmetic may be done from the RUN-MAT screen or from the CAS
screen. The RUN-MAT screen provides answers in decimal form; whereas, the CAS
screen gives exact answers. To access a screen, press **MENU**,
then press **1** for the RUN-MAT screen or press **9** for the CAS screen.
For example, we display (6 – 3*i*)/(4 + 5*i*) from
the RUN-MAT screen (below, left) and from the CAS screen (below, right).