How to find all complex Z such that Z^5=-32

  • Thread starter grossgermany
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In summary, in order to find all complex numbers Z such that Z^5=-32, we can express -32 in polar form and use de Moivre's formula to find the roots by multiplying the arguments by 1/5. This will give us five distinct roots before they start repeating.
  • #1
grossgermany
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Homework Statement


How to find all complex number Z such that Z^5=-32


Homework Equations


Euler equation
e^it=cost+isint


The Attempt at a Solution


I guess a naive way to solve is that since Z^5=(-2)^5
Therefore Z=-2, but this obviously too good to be true.
I have no background in complex analysis.
 
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  • #2
Z=(-2) isn't too good to be true. You are right. It is a root. But there are four more. Express -32 in polar form. I.e. -32=32*e^(it). The use deMoivre. What are the possibilities for t? There are more than one. Give me one to start out with.
 
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  • #3
Thank you for your reply.
Sorry I do not understand that -32=32*e^(it)?
e^it=cost+isint
I mean t is a variable that takes on arbitrary values.
 
  • #4
grossgermany said:
Thank you for your reply.
Sorry I do not understand that -32=32*e^(it)?
e^it=cost+isint
I mean t is a variable that takes on arbitrary values.

t isn't arbitrary if -32=32*e^(it). That means e^(it)=(-1). What's t?
 
  • #5
t=180degree=-5pi,-3pi,-pi,pi,3pi,5pi,7pi,9pi,11pi?
Therefore -32=32*e^(it)=32*[cos(pi)+isin[pi]]

Sorry how do I use de Moivre's formula? Never taken complex analysis
 
  • #6
grossgermany said:
t=180degree=-5pi,-3pi,-pi,pi,3pi,5pi,7pi,9pi,11pi?
Therefore -32=32*e^(it)=32*[cos(pi)+isin[pi]]

Sorry how do I use de Moivre's formula? Never taken complex analysis

You could look it up rather than me telling you. You multiply the arguments (the angles) by 1/5. How many roots do you get before they start repeating?
 
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1. How do I solve for complex Z in the equation Z^5=-32?

To solve this equation, you can use the fifth root property. Take the fifth root of -32, which is -2, and then multiply it by the fifth root of 1, which is 1. The fifth root of 1 is 1 because any number raised to the power of 0 is equal to 1. This will give you the value of Z, which is -2.

2. Can I use the quadratic formula to solve this equation?

No, the quadratic formula can only be used for equations in the form of ax^2+bx+c=0. Since this equation is in the form of Z^5=-32, the quadratic formula cannot be used.

3. Are there multiple values of Z that satisfy this equation?

Yes, there are multiple values of Z that satisfy this equation. In fact, there are five different complex solutions for Z: -2, 1+1.732i, 1-1.732i, -1+1.732i, and -1-1.732i.

4. How do I know if my solution for Z is correct?

You can check your solution by plugging it back into the original equation. If your solution is correct, it should make the equation true. For example, if your solution for Z is -1+1.732i, then (-1+1.732i)^5 should equal -32.

5. Can I use a calculator to solve this equation?

Yes, you can use a calculator to find the solutions for Z. Most scientific calculators have a fifth root function that you can use to find the complex solutions. However, it is important to understand the concept behind the solution and not solely rely on a calculator for solving equations.

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