(I'm going to use 0.5 instead of 1/2 to make things easier for me.)
(x+0.5) is a factor of a polynomial if it divides evenly (IOW the remainder is zero) into the polynomial. So all we have to do is divide the polynomial by (x+0.5) and see if the remainder is zero:
-0.5 | 10 9 -4 9 6
------ -5 -2 3 -6
---------------------
10 4 -6 12 0
The remainder is 0. So (x + 0.5) is a factor of P(x). (The other factor, taken from the numbers in front of the remainder, is