Problem from past PGRE: A particle of mass m moves in a one-dimensional potential V(x)=-ax2 + bx4, where a and b are positive constants. The angular frequency of small oscillations about the minima of the potential is equal to: Answer is 2(a/m)1/2. I understand how this is found 'the long way' by actually applying calculus, but if you plug in a=-1/2 k and b=0 shouldn't you get back sqrt(k/m) ? Because the harmonic potential is 1/2kx^2 ... so where is the flaw in my logic? Thanks!