Math Problem Statement

Solve the mcq

If imaginary cubic roots of unity is ω = (-1 + √3i) / 2, then i. ω^10 = ω, ii. |ω| = 1, iii. arg ω = 2π/3. Which one of the following is correct? a. i and ii b. ii and iii c. i and iii d. i, ii and iii

Solution

Let's analyze the problem step-by-step:

Problem Summary:

We have an imaginary cubic root of unity given as: ω=1+3i2\omega = \frac{-1 + \sqrt{3}i}{2} The task is to evaluate the given statements about ω\omega:

  1. ω10=ω\omega^{10} = \omega
  2. ω=1|\omega| = 1
  3. arg(ω)=2π3\arg(\omega) = \frac{2\pi}{3}

We need to check which of these statements is correct.

Step 1: Understanding ω\omega

The cubic roots of unity are the solutions to the equation x3=1x^3 = 1. These roots are:

  1. 11 (the real root),
  2. ω=1+3i2\omega = \frac{-1 + \sqrt{3}i}{2}, and
  3. ω2=13i2\omega^2 = \frac{-1 - \sqrt{3}i}{2}.

These roots satisfy: ω3=1andω2+ω+1=0.\omega^3 = 1 \quad \text{and} \quad \omega^2 + \omega + 1 = 0.

Step 2: Evaluate Each Statement

Statement (i): ω10=ω\omega^{10} = \omega

Since ω3=1\omega^3 = 1, we can use this property to simplify powers of ω\omega: ω10=ω3×3+1=(ω3)3ω=1ω=ω.\omega^{10} = \omega^{3 \times 3 + 1} = (\omega^3)^3 \cdot \omega = 1 \cdot \omega = \omega. So, Statement (i) is correct.

Statement (ii): ω=1|\omega| = 1

The modulus of ω=1+3i2\omega = \frac{-1 + \sqrt{3}i}{2} is: ω=(12)2+(32)2=14+34=1=1.|\omega| = \sqrt{\left(\frac{-1}{2}\right)^2 + \left(\frac{\sqrt{3}}{2}\right)^2} = \sqrt{\frac{1}{4} + \frac{3}{4}} = \sqrt{1} = 1. So, Statement (ii) is correct.

Statement (iii): arg(ω)=2π3\arg(\omega) = \frac{2\pi}{3}

To find the argument of ω\omega, we observe that ω\omega is in the second quadrant (since it has a negative real part

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Roots of Unity
Cubic Roots of Unity

Formulas

ω = (-1 + √3i) / 2
ω^3 = 1
Modulus of a complex number |z| = √(Re(z)^2 + Im(z)^2)
Argument of a complex number arg(z) = θ

Theorems

Properties of roots of unity

Suitable Grade Level

Grades 11-12