Finding powers of complex numbers is greatly simplified using
De Moivre’s Theorem . It states that, for a positive integer
is found by raising the modulus to the
power and multiplying the argument by
It is the standard method used in modern mathematics.
De moivre’s theorem
If
is a complex number, then
where
is a positive integer.
Evaluating an expression using de moivre’s theorem
Evaluate the expression
using De Moivre’s Theorem.
Since De Moivre’s Theorem applies to complex numbers written in polar form, we must first write
in polar form. Let us find
Then we find
Using the formula
gives
Use De Moivre’s Theorem to evaluate the expression.
To find the
n th root of a complex number in polar form, we use the
Root Theorem or
De Moivre’s Theorem and raise the complex number to a power with a rational exponent. There are several ways to represent a formula for finding
roots of complex numbers in polar form.
The
n Th root theorem
To find the
root of a complex number in polar form, use the formula given as
where
We add
to
in order to obtain the periodic roots.
Questions & Answers
A laser rangefinder is locked on a comet approaching Earth. The distance g(x), in kilometers, of the comet after x days, for x in the interval 0 to 30 days, is given by g(x)=250,000csc(π30x). Graph g(x) on the interval [0, 35]. Evaluate g(5) and interpret the information. What is the minimum distance between the comet and Earth? When does this occur? To which constant in the equation does this correspond? Find and discuss the meaning of any vertical asymptotes.
