Find all critical points of f(x)=x4−8x2f(x) = x^4 - 8x^2f(x)=x4−8x2 and classify them.
Local max at x=0x=0x=0; local min at x=±2x=\pm 2x=±2
Local min at x=0x=0x=0; local max at x=±2x=\pm 2x=±2
Only local min at x=±2x=\pm 2x=±2; x=0x=0x=0 is inflection
Local min at x=0x=0x=0; saddle points at x=±2x=\pm 2x=±2