1. The problem statement, all variables and given/known data Look below. 2. Relevant equations So my book says that you have a conservative system when E'(t) = [(1/2)m(x'(t))2 + V(x(t))]'(t) = 0. It gives an example of V(x) = -(1/2)x2 + (1/4)x4, whence setting y = x' gives E = (1/2)y2 -(1/2)x2 + (1/4)x4. According to the book, E = constant. Not sure how they got this since E' ≠ 0 as far as I can tell. 3. The attempt at a solution Me no understand.