radu <rraduconstantin@gmail.com> wrote in message news:kd92ed$mnf$1@newscl01ah.mathworks.com...> Hello,>> I have this equation: f:= a*x^2 + b>> how can i derivate this with rapport to the time just around x using a and > b as constants.Unless you have specified that x is a function of t, f is constant with respect to t and so the derivative WRT time should be 0.> this i