relative extrema: f has a relative maximum at x=-1,
and f has a relative minimum at x=1. The interval that
f is concave up or concave down: We observe Therefore
the function f is concave upward on
and concave downward on
The inflection points of f are at
and
For graph, use plot(3*x^5-5*x^3,x=-2..2,y=-5..5, thickness=3); Pay
attention the intervals where f is concave upward or downward.