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