can someone show me the steps to work out this problem that is diving me nuts..

Directions: Find all positive values for k for which each of the following can be factored.

x^2+x-k

I am completely cluelis towards this problem....i've tried it many different ways....

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

Now if you are restricting the x to the real number system, then k can be any postive number.

The factors will be
(x+1/2-1/2 sqrt(1+4k) ) and (x+1/2
+1/2 sqrt(1+4k)) for any value of k>0

can you explain how to get there because i still don't understand