E = (x2+x3)/x1 + (x1+x3)/x2 + (x1+x2)/x3
x³-6x²+x+2 = 0
x1+x2+x3 = 6
=> x2+x3 = 6-x1
=> x1+x3 = 6-x2
=> x1+x2 = 6-x3
E = (6-x1)/x1+(6-x2)/x2+(6-x3)/x3
E = 6/x1 - 1 + 6/x2 - 1 + 6/x3 - 1
E = 6•(1/x1 + 1/x2 + 1/x3) - 3
E = 6•((x2x3+x1x3+x1x2)/(x1x2x3) - 3
E = 6•(1/(-2)) - 3
E = -3-3 = -6