An n'th order polynomial will have n roots, some of which may be repeated or complex. You have a 3rd order polynomial which will have 3 roots. Turns out one of the roots is real and the other two are complex (meaning a plot of the polynomial will only cross the x-axis once). If you plug the roots into the polynomial you can see that all three results are very close to zero as expected:
>> f = @(x) 0.5*x.^3 + x.^2 - 10*x + 14.037
f =
@(x)0.5*x.^3+x.^2-10*x+14.037
>> r = roots ([0.5 1 -10 14.037])
r =
-6.062670505918885
2.031335252959442 + 0.710147689980882i
2.031335252959442 - 0.710147689980882i
>> f(r)
ans =
1.0e-013 *
0.230926389122033
0.035527136788005 - 0.062172489379009i
0.035527136788005 + 0.062172489379009i
Look at it this way, if you take your real root and form (x+6.062670505918885) and factor that out of your polynomial, you will be left with a 2nd order polynomial that has no real roots.