Find the x-values for which f '(x) = 0 in the given interval. (enter your answers as a comma-separated list. if an answer does not exist, enter dne.) f '(x) = 6x2 − 24x − 30 = 0 x = 5,−1 note that since f(x) is defined on a closed interval, f '(x) cannot exist at the endpoints of the interval because the definition of the derivative at a point requires the existence of a two-sided limit. find the x-values for which f '(x) is undefined in the given interval. (enter your answers as a comma-separated list. if an answer does not exist, enter dne.) f '(x) is undefined when x = −1 . thus, the potential extreme points of f(x) in the given interval are x =