Math Problem Statement

Find the fourth roots of z = -√3 + i.

Solution

To find the fourth roots of z=3+iz = -\sqrt{3} + i, we need to use the nth root theorem. Here are the steps:

Step 1: Convert zz to Polar Form

  1. Determine the modulus rr: r=(3)2+(1)2=3+1=4=2r = \sqrt{(-\sqrt{3})^2 + (1)^2} = \sqrt{3 + 1} = \sqrt{4} = 2

  2. Determine the argument θ\theta: Since z=3+iz = -\sqrt{3} + i is located in the second quadrant (negative real, positive imaginary), we find θ\theta by calculating: tan1(13)=tan1(13)=π6\tan^{-1}\left(\frac{1}{-\sqrt{3}}\right) = \tan^{-1}\left(-\frac{1}{\sqrt{3}}\right) = -\frac{\pi}{6} However, to place it correctly in the second quadrant, we add π\pi: θ=ππ6=5π6\theta = \pi - \frac{\pi}{6} = \frac{5\pi}{6}

Thus, the polar form of zz is: z=2(cos5π6+isin5π6)z = 2 \left( \cos\frac{5\pi}{6} + i \sin\frac{5\pi}{6} \right)

Step 2: Apply the nth Root Theorem for Fourth Roots

For the fourth roots, we calculate: wk=24(cos5π6+2kπ4+isin5π6+2kπ4)w_k = \sqrt[4]{2} \left( \cos\frac{\frac{5\pi}{6} + 2k\pi}{4} + i \sin\frac{\frac{5\pi}{6} + 2k\pi}{4} \right) where k=0,1,2,3k = 0, 1, 2, 3.

Would you like a detailed calculation for each root?

Here are five related questions to expand your understanding:

  1. How would you find the square root instead of the fourth root for this complex number?
  2. What would the polar form of z=3+iz = -\sqrt{3} + i be if it were located in a different quadrant?
  3. Can you explain why we add π\pi to adjust the argument in the second quadrant?
  4. How would you apply the nth root theorem if the modulus of zz were a different value?
  5. How can you verify each root obtained from the nth root theorem?

Tip: When converting a complex number to polar form, always check the quadrant to ensure the argument is placed correctly.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Polar Form Conversion
Roots of Complex Numbers

Formulas

Modulus of a complex number: r = √(a^2 + b^2)
Argument of a complex number: θ = tan^(-1)(b/a)
Polar form: z = r (cos θ + i sin θ)
Nth root theorem: w_k = √[n]{r} (cos((θ + 2kπ)/n) + i sin((θ + 2kπ)/n))

Theorems

Nth Root Theorem

Suitable Grade Level

Grades 10-12