Well , are you familiar with the factor theorem ?
If not , note that for a polynomial P(x),(x-a) is a factor of P(x) if and only if P(a)=0 .
Notice that the constant term for the equation above is -6 .
Hence if (x-a) were to be a factor of P(x) , then a must be a factor of -6.
If x=1 , P(1)=1+2-5-6=-8 , hence (x-1) is NOT a factor .
If x=-1,P(-1)=-1+2+5-6=0 , hence (x+1) IS a factor .
Try doing this for all values of a stated above and you should get all the factors for this equation .