Sigma Percentile
JEE Advanced 2004S
LEVELJEE Main

Animated Solution for Mathematics - Complex Numbers: If be a cube root of unity and , then the least positive value of is

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Visualized Solution

Visualizing Cube Roots of Unity

  • Given: is a cube root of unity.
  • Equation: .
  • Goal: Find the least positive integer .

The Sum Property:

  • Fundamental Property: .
  • This implies the sum of all cube roots of unity is zero.

Simplifying the LHS

  • From the sum property, rearrange to get: .
  • Substitute this into the Left Hand Side (LHS).
  • LHS becomes: .

The Power Property:

  • Property: The product of the roots is , so .
  • We will use this to reduce higher powers of .

Simplifying

  • Break down into smaller powers.
  • .
  • Since , this simplifies to .

Simplifying the RHS

  • The Right Hand Side (RHS) is now .
  • Using the sum property, .
  • Substitute this to get RHS: .

Equating Both Sides

  • Equate the simplified LHS and RHS.
  • .

Rearranging the Equation

  • Divide both sides by .
  • This gives: .

Applying Exponent Laws

  • Using the law , we get .
  • The negative signs cancel, and .
  • The equation simplifies to: .

Finding the Least Positive

  • We need the smallest positive integer such that .
  • Since , the least positive value is .
  • Final Answer: .

The Sigma Insight: Cube Roots and nth Roots of Unity

Solution Diagram

Analyzing the Setup

The cube roots of unity, denoted as , , and , are geometric anchors on the complex plane. They are perfectly spaced at intervals on the unit circle.
Our primary objective is to solve the equation:

The Master Identity

The most powerful tool in our arsenal is the fundamental identity:
This identity arises because the sum of the roots of the polynomial is zero, as there is no term in the expansion.

Simplifying the LHS and RHS

First, we simplify the Left Hand Side (LHS). Using the identity , the expression becomes:
Next, we simplify the Right Hand Side (RHS). Since , we know that . Applying the identity , the expression becomes:

Solving for

Equating the simplified sides, we have:
Dividing both sides by , we obtain:
Using the laws of exponents, this simplifies to:

Final Calculation

We are looking for the least positive integer such that . Given the property , the smallest positive integer that satisfies this condition is:

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