ok here we go...

the rate of change of N with respect to S is proportional to 500 - S

so the set up is pretty straight forward...

I got dN/dS = k(500 - S)

when i integrated it i got N = 500S - (S)^2/2 + C, the book said something different..which is where im confused..

books answer: N = -k/2(500 - S)^2

please explain, thanks in advance....