Is x^2+x-k Factorable?

I have spent way too much time trying to find to factor this triominal and starting to belive it is not factorable. Is this correct?

Here are the factors:

(x+(1+sqrt(1+4k))/2)
(x+(1 -sqrt(1+4k) )/2)

You ought to recognize where these came from: the quadratic equation