Numerical differentiation, fsolve or forward differentiation

Hello!

I have a function V(see below) where all the values except theta(θ) are known. I need to calculate and plot dv/dθ numerically for 0<=θ<=90 and find the values of θ when V=0. Is using fsolve a good alternative to using forward/backward differentiation. I need some tips to get started!

V=0.5*k*l^2*sind(theta).^2+0.5*m*g*l*cosd(theta);% my function

[Torsten]

I don't understand why you think that finding the roots of v (finding the values of theta where v=0) has anything to do with calculating and plotting dv/d(theta). Or do you want to program Newton's method with numerical derivatives ?

Best wishes

Torsten.