4. [0/0.05 Points] DETAILS PREVIOUS ANSWERS For what values of x does the graph of f(x) = x + 2x2 + x + 4 have a horizontal tangent? X (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.) X 5. [0.04/0.05 Points] DETAILS PREVIOUS ANSWERS Let f( x ) = x +- 25 - + 4. X (a) Find the domain of f. (Enter your answer using interval notation.) The domain of fis (-00,0) U (0,00) (b) Find the derivative of the function f. 25 f' ( x ) = (c) Find the domain of f' . (Enter your answer using interval notation.) The domain of f ' is (-00,0) U (0,00) (d) Determine the value(s) of x in the domain of f, if any, at which the function is not differentiable. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.) X = dne (e) For what values of x does the graph of f have a horizontal tangent? (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.) X X