Let f(x)= -x^4-7x^3+8x+3.
(A) Use interval notation to indicate where is concave up.
Note: Use 'INF' for , '-INF' for , and use 'U' for the union symbol.
(B) Use interval notation to indicate where f(x) is concave down.
(C) List the values of all the inflection points of . If there are no inflection points, enter 'NONE'.
values of inflection points =