Identify the open intervals on which the graph of the function is concave upward or concave downward. Assume that the graph extends past what is shown. 6- 14 - -10 -8 6 -4--20 2 4 6 -2 * 4- 8. Note: Use the letter U for union. To enter co, type infinity. Enter your answers to the nearest integer. If the function is never concave upward or concave downward, enter NA in the associated response area. concave upward: concave downward