Jika akar² PK 2x²+9x -4 adalah α dan β, maka α³ + β³ adalah?

2x²+9x -4 = 0
A = 2
B = 9
C = - 4

α + β = -B/A= -9/2
α.β = C/A = -4/2 = -2

α³ + β³ = (α+ β)³ - 3(α + β)(α β)
= (-9/2)³ - 3(-9/2)(-2)
= -729/8 - 27
= -391,5