This may be a dumb question to those who have experience with ODEs but I cant figure out how to answer the following questions:

Is 0 a stable equilibrium of $\displaystyle x''(t) + 2x^3(t) = 0$?

Is 0 an asymptotically stable equilibrium of $\displaystyle x''(t) + 2x^3(t) = 0$?

I'm familiar with the definition of a stable equilibrium but I seem to have a mental block when it comes to figuring these out. Any help would be much appreciated.