persamaan kuadrat x2 + ax + b = 0 dengan b tidak sama dengan 0 mempunyai akar-akar 2a dan 2b, maka a3 + b3 =...

x^2 + ax + b = 0
x1 = 2a dan x2 = 2b

x1.x2 = c/a
(2a)(2b) = b
4ab = b
a = b/4b = 1/4

x1 + x2 = -b/a
(2a) + (2b) = -a
2b = -3a
b = (-3/2)a = (-3/2)(1/4) = -3/8

a^3 + b^3 = (1/4)^3 + (-3/8)^3 = 1/64 - 27/512 = (8 - 27)/512 = -19/512