Hahaha welcome back FS!
Btw, isn' finding derivative differentiating the eqn, not
integrating it (which was what you did)?
I thought it would be like
P(x) = 6x - (x^2 / 1000) - 500
P(x) ' = 6 - x/500
Do enlighten me o.0
You are right : ( Integrand then is integrate.
Careless mistake, need to read carefully next time
round.
And to FI rox, if you differentiate again, it will become
-1/500