g(x) = 1/5·x^3 - 16/5·x
g'(x) = 3/5·x^2 - 16/5
n(x) = -1/g'(0) * (x - 0) + g(0) = 0.3125·x
A = 1/2 * (g(u) - n(u)) * u = 1/2 * (1/5·u^3 - 16/5·u - 0.3125·u) * u = 0.1·u^4 - 1.75625·u^2
A' = 0.4·u^3 - 3.5125·u = 0 --> u = 2.963
A = 0.1·2.963^4 - 1.75625·2.963^2 = -7.711034802
Die max. Fläche beträgt 7.711 FE.