# Thread: Multiplication of complex exponential numbers

1. ## Multiplication of complex exponential numbers

(625e^(3.46i))*(4.4e^(1.22i))

when i multiply it out i get 2750e^(4.2212i) From there I'm supposed to make it into polar and rectangular forms. the answers in the book are 2750(cos268.1 degrees + i*sin268.1 degrees) for polar form and -89.1 -2750i for rectangular form. Both my answers were incorrect according to the book. So my multiplication must have been off, if anyone can check it for me please.

2. Originally Posted by OzzMan
(625e^(3.46i))*(4.4e^(1.22i))

when i multiply it out i get 2750e^(4.2212i) From there I'm supposed to make it into polar and rectangular forms. the answers in the book are 2750(cos268.1 degrees + i*sin268.1 degrees) for polar form and -89.1 -2750i for rectangular form. Both my answers were incorrect according to the book. So my multiplication must have been off, if anyone can check it for me please.

First $\displaystyle 3.46+1.22=4.68$ not $\displaystyle 4.22$, so you should have: $\displaystyle 2750 e^{4.22i}$ since:

$\displaystyle (625e^{3.46i})\times (4.4e^{1.22i})=625 \times 4.4 \times e^{(3.46+1.22)i}$

and $\displaystyle 4.46$ radian is $\displaystyle 268.1$ degrees (rounded to that precission).

Of course you should also know that:

$\displaystyle e^{i \theta}=\cos(\theta)+i \sin(\theta)$

RonL

3. woops i multiplied exponents.