Find the critical numbers of f in the open interval(4,4). (Enter your answers as a comma-separated list.) x =?

Find the critical numbers of f in the open interval (−4, 4). (Enter your answers as a comma-separated list.)

x = ?

Find the open interval(s) on which f ' is positive and the open interval(s) on which f ' is negative. (Enter your answers using interval notation.)

positive ?

negative ?