How to Solve z^3 = -8 in Complex Numbers?

In summary, to find all complex numbers satisfying z^3=-8, you can think of -8 as -8 + 0i and convert it into polar coordinates using the formula -8=8(cos0+isin0). Then, using the polar form z=rexp(ix), you can find the three roots on the circle with radius r=(-8)^(1/3). Alternatively, you can use D'Moivre's theorem or the cube roots of unity to solve for the three roots. Factor theorem can also be used.
  • #1
sara_87
763
0
find all complex numbers satisfying z^3=-8
i have no idea how to solve this can someone help please?
thank u
 
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  • #2
Think -8 as -8 + 0i... Then convert this into polar coordinates.
 
  • #3
in polar coordinates it will be:
-8=8(cos0+isin0)
giving
-8=8
?
 
  • #4
i think that if you write down z=rexp(ix) would be easier...
you find three roots on the cricle with radius r=(-8)^(1/3).

bye
marco
 
  • #5
Are you saying you have been asked to find cuberoots and have never heard of D'Moivre's theorem? Why that's awful! Almost as bad posting a homework problem under the mathematics thread!
 
  • #6
He actually doesn't need D'Moivre's theorem, only the three cube roots of unity.

Hi sara_87,

Have you done the complex cube roots of one in class? You know, omega, omega^2 etc.? Show some work.
 
  • #7
Or just basic remainder and factor theorem...f(z)=z^3+8=0. But the other ways are faster.
 

FAQ: How to Solve z^3 = -8 in Complex Numbers?

What is a complex number?

A complex number is a number that consists of a real part and an imaginary part. It is written in the form a + bi, where a is the real part and bi is the imaginary part, with i being the imaginary unit equal to the square root of -1.

How do you solve a complex number equation?

To solve a complex number equation, first rewrite it in the form z = a + bi. Then, use the cubic formula z = ∛r(cosθ + isinθ), where r is the magnitude of z and θ is the angle between z and the positive real axis. Finally, substitute the values of r and θ into the formula to find the three possible solutions for z.

What is the cube root of -8?

The cube root of -8 is -2, since (-2)^3 = -8.

How many solutions can a complex number equation have?

A complex number equation can have up to three solutions, since a cubic equation has three roots. However, some solutions may be repeated or may not be real numbers.

Can complex numbers be graphed on a number line?

No, complex numbers cannot be graphed on a number line since they have both real and imaginary components. They can be graphed on a complex plane, with the real part on the x-axis and the imaginary part on the y-axis.

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