What the syllabus doesn't tell you is that the second and third derivative tests can be generalised:
Successive derivative test:
If f<sup>(n)</sup>(x<sub>0</sub>)=0 for n=2,3,4,...,2k and if f<sup>(2k+1)</sup>(x<sub>0</sub>) exists and ≠0 then (x<sub>0</sub>, f(x<sub>0</sub>)) is an...