Критические точки - это точки, в которых производная равна 0
f ' (x) = -x^4 + x^2 = 0
x^2*(-x^2 + 1) = x^2*(1 + x)(1 - x) = 0
x1 = -1; f(-1) = 1/5 - 1/3 - 17 13/15 = (3 - 5)/15 - 17 13/15 = -2/15 - 17 13/15 = -18
x2 = x3 = 0; f(0) = -17 13/15
x4 = 1; f(1) = -1/5 + 1/3 - 17 13/15 = (-3 + 5)/15 - 17 13/15 = 2/15 - 17 13/15 = -17 11/15
Наименьшая точка x1 = -1; f(-1) = -18