If a force F is defined by F=k(e^(-s) -6e^(-2s)), where S is the distance between two objects, then prove (d^(2)F)/(d(S)^2)=F-18ke^(-25).

I'm not sure what d^2 is supposed to mean.. does it mean take the derivative and square it?

Well I did take the derivative.. did not square it yet. Don't know if this is right but gave it a shot:

(d^(2)F)/(dS^2)=-e^-s -6e^(-2s)+k(-e^(-s) -6e^(-2s) (-2))

=e^-s(-6e^-2s+k(12e^-2s-e^-s)