a + b + c = 0a+b+c=0
LHS = (a + bω + cω²)³ + (a + bω² + cω)³
If we consider A = (a + bω + cω²) and B = (a + bω² + cω)
Adding the two.
color(magenta)(A + B) = 2a + b(omega+omega^2) + c(omega^2 +omega)
=> 2a-b-c = 3a-a-b-c = 3a-0 = color(magenta)(3a) "as " [ω² + ω + 1 = 0]
Multiplying the two
color(magenta)(AB) = (a + b + c)² - 3(ab + bc + ca) = color(magenta)(- 3(ab + bc + ca)
As we know, (A+B)^3 = A^3+B^3 +3AB(A+B)
P => A^3+B^3 = (A + B)³ - 3AB(A + B)
= 27a³ + 27a(ab + bc + ca)
= 27a(a² + ab + ac + bc) = 27a(a + b)(a + c) = 27a(-c)(-b) = 27abc