28.

Determine where the given function is concave up and where it is concave down f (x ) = x4 - 24x2 A. Concave down on ( - co, - 2) and (2, co), concave up on ( - 2, 2) O B. Concave up on ( - co, - 2) and (0, 2), concave down on ( - 2, 0) and (2, co) O C. Concave up on ( - co, - 2) and (2, co), concave down on ( - 2, 2) O D. Concave up on ( - co, - 21/3) and (213, co), concave down on ( - 21/3, 21/3)