(1 point) NOTE: When using interval notation in WeBWorK, remember that: You use 'INF' for 00 and '-INF' for 00. And use 'U' for the union symbol. Enter DNE if an answer does not exist. at) 2 $4111.13, at: > 0. a) Determine the intervals on which f is concave up and concave down. f is concave up on: f is concave down on: b) Based on your answer to part (a), determine the inection points of 1'. Each point should be entered as an ordered pair (that is, in the form (x, 3,0). (Separate multiple answers by commas.)