3x+2x+6=0 dengan akar-akarnya alfa dan beta (alfa pangkat tiga +beta pangkat tiga):(1/alfa +1/beta)

alfa = a
beta = b
dimana :
a + b = -2/3
ab = 6/3 = 2

(a³ + b³) : (1/a + 1/b)
= {(a+b)³ - 3ab(a+b)} : {(a+b)/ab}
= {(-2/3)³ - 3(2)(-3/2)} : {(-2/3)/(2)}
= {(-8/27) + 9} : (-2/6)
= {(-8/27) + (243/27)} × -6/2
= (235/27) × -3
= -235/9