Complex Roots of Equations: Solving z^3 = -8i

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In summary, the conversation discusses the problem of solving the equation z^3=-8i and suggests two methods, one using De Moivre's theorem and another using the concept of finding the cube root of -8i. The conversation also mentions considering all the possible values of theta as the unit circle is rounded once.
  • #1
littlewombat
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De Moivre's theorem~~HELP~

Homework Statement



Solve the following equations


z^3=-8i


Can anyone please tell me how to solve this problem?
 
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  • #2


You can use De Moivre's theorem (actually, are you meant to?) but there is an easier way to solve it.

Notice that [tex]-8i=\left(2i\right)^3[/tex]
 
  • #3


littlewombat said:

Homework Statement



Solve the following equationsz^3=-8iCan anyone please tell me how to solve this problem?

Z=cuberoot(-8i)

So write (-8i) in r*e^(i*theta) form and then raise it to the one-third...then consider all the angles that theta could be as you round the unit circle once.

EDIT: I like Mentallic's way, haha.
 
  • #4


Apphysicist said:
EDIT: I like Mentallic's way, haha.

Haha thanks :approve:
 

What is De Moivre's theorem?

De Moivre's theorem is a mathematical formula that relates complex numbers and trigonometric functions. It states that for any complex number z and integer n, the nth power of z can be represented as the product of the nth root of z and the nth power of the complex number (cos θ + i sin θ), where θ is the angle formed by z and the positive real axis.

How is De Moivre's theorem used in mathematics?

De Moivre's theorem is used in a variety of mathematical applications, such as simplifying complex numbers, finding roots of complex numbers, and solving differential equations. It also has applications in physics, engineering, and other fields.

Who discovered De Moivre's theorem?

The theorem is named after French mathematician Abraham de Moivre, who first published it in his book "The Doctrine of Chances" in 1730. However, it was also independently discovered by Swiss mathematician Johann Bernoulli.

What is the significance of De Moivre's theorem?

De Moivre's theorem provides a powerful tool for working with complex numbers and has many practical applications in various fields of mathematics. It also allows for the simplification and generalization of many mathematical problems.

Are there any limitations to De Moivre's theorem?

De Moivre's theorem is limited to working with complex numbers and cannot be applied to real numbers. It also has some restrictions in terms of the values of n and θ that can be used. Additionally, it only applies to certain types of functions and may not work for all mathematical problems.

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