Maxima and Minima are characterized by a zero derivative. We may use this to get all extrema:
Apa[x_] := x Cos[\[Pi]/6] (x^5 - 2 x^3 + x) - 0.08;ext = x /. {Reduce[Apa'[x] == 0, x] // ToRules}{-1, 0, 1, -(1/Sqrt[3]), 1/Sqrt[3]}With this:
Plot[Apa[x], {x, -1.5, 1.5}, Epilog -> Point[{#, Apa[#]} & /@ ext]]
