Cube roots of unity: 1, w, w^2 where w = (-1+isqrt(3))/2 = e^(2pi*i/3).
Fundamental Properties:
- w^3 = 1 and 1 + w + w^2 = 0
- w^2 = w-bar (they are conjugates)
- |w| = |w^2| = 1
- w^(-1) = w^2
Simplification Substitutions:
- 1 + w = -w^2 (most used substitution)
- 1 + w^2 = -w
- w + w^2 = -1
Useful Products:
- (1-w)(1-w^2) = 3
- (1+w)(1+w^2) = 1
- (a+bw+cw^2)(a+bw^2+cw) = a^2+b^2+c^2-ab-bc-ca
Factorizations:
- x^2+x+1 = (x-w)(x-w^2)
- x^3-1 = (x-1)(x-w)(x-w^2)
- a^3+b^3+c^3-3abc = (a+b+c)(a+bw+cw^2)(a+bw^2+cw)
Power Reduction: For any integer n, w^n = w^(n mod 3). This converts any power of w to one of {1, w, w^2}.
JEE Problem Strategy: When you see w in a problem:
- Immediately write 1+w+w^2 = 0
- Reduce all powers mod 3
- Replace 1+w with -w^2 (or similar)
- Simplify using w^3 = 1
These identities appear in determinants, binomial coefficients, and algebraic expression problems. Master the substitutions to solve in 30-60 seconds.