Multiplying Complex Numbers

Algebra 2 Tutorial

Multiplying Complex Numbers

Intro

We wish to multiply two complex numbers, say (a+bi)(c+di)
We will use the FOIL method: First Outer Inner Last.

********************************************
PLOT
(PL)(OT)
(PO) + (PT) + (L0) + (LT)
F…………O…………I…………L
your plot has been foiled :)
********************************************

Sample Problem

Let’s say we want to multiply
(3+4i) by (-2+6i)

Solution

(3+4i)(-2+6i)
3x(-2) + 3x6i + 4ix-2 + 4ix6i …..using foil
-6 + 18i -8i -24 ……..(4ix6i) is negative because
……………………………………………i squared is negative 1
-30 + 10i
so

(3+4i)(-2+6i) = (-30+10i)



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