Math Problem Statement

Solve z^4 = 8 + 8√3i.

Solution

The equation in the image is:

z4=8+83iz^4 = 8 + 8\sqrt{3}i

This is a complex number equation that we need to solve for zz. We can solve it using polar form and De Moivre's Theorem. Here's the step-by-step process:

Step 1: Express the right-hand side in polar form

The complex number 8+83i8 + 8\sqrt{3}i can be written in polar form r(cosθ+isinθ)r(\cos \theta + i \sin \theta), where:

  • rr is the modulus,
  • θ\theta is the argument (angle).

Modulus:

r=82+(83)2=64+192=256=16r = \sqrt{8^2 + (8\sqrt{3})^2} = \sqrt{64 + 192} = \sqrt{256} = 16

Argument:

θ=tan1(838)=tan1(3)=π3\theta = \tan^{-1} \left( \frac{8\sqrt{3}}{8} \right) = \tan^{-1}(\sqrt{3}) = \frac{\pi}{3}

So the polar form is: 16(cosπ3+isinπ3)16 \left( \cos \frac{\pi}{3} + i \sin \frac{\pi}{3} \right)

Step 2: Apply De Moivre's Theorem

To solve z4=16(cosπ3+isinπ3)z^4 = 16 \left( \cos \frac{\pi}{3} + i \sin \frac{\pi}{3} \right), we take the fourth root of both sides.

The fourth root of the modulus r=16r = 16 is: 164=2\sqrt[4]{16} = 2

The argument is divided by 4: π3+2kπ4=π12+kπ2,k=0,1,2,3\frac{\frac{\pi}{3} + 2k\pi}{4} = \frac{\pi}{12} + \frac{k\pi}{2}, \quad k = 0, 1, 2, 3

So the four solutions for zz are:

zk=2(cos(π12+kπ2)+isin(π12+kπ2)),k=0,1,2,3z_k = 2 \left( \cos \left( \frac{\pi}{12} + \frac{k\pi}{2} \right) + i \sin \left( \frac{\pi}{12} + \frac{k\pi}{2} \right) \right), \quad k = 0, 1, 2, 3

These are the four roots in polar form.

Would you like to see the detailed steps for each solution?


Here are 5 related questions to explore this topic further:

  1. What is De Moivre's Theorem and how is it used in solving complex number equations?
  2. How do you convert a complex number from rectangular form to polar form?
  3. What are the different methods for solving higher-degree equations in complex numbers?
  4. How does the modulus and argument of a complex number affect its polar representation?
  5. How can you geometrically interpret the four roots of the equation z4=8+83iz^4 = 8 + 8\sqrt{3}i?

Tip: Always check the quadrant of the complex number to get the correct argument θ\theta when converting to polar form.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Polar Coordinates
Roots of Complex Numbers

Formulas

Modulus of complex number: r = √(a^2 + b^2)
Argument of complex number: θ = tan⁻¹(b/a)
De Moivre's Theorem: z^n = r^n(cos(nθ) + i sin(nθ))

Theorems

De Moivre's Theorem

Suitable Grade Level

Undergraduate level, advanced high school