For \( f ( x ) = x ^ { 4 } - 4 x ^ { 3 } + 6 \) find the following. (A) \( f ^ { \prime } ( x ) \)
(B) The slope of the graph of \( f \) at \( x = 1 \) (C) The equation of the tangent line at \( x = 1 \) (D) The value(s) of \( x \) where the tangent line is horizontal (A) \( f ^ { \prime } ( x ) = 4 x ^ { 3 } - 12 x ^ { 2 } \)
(B) At \( x = 1 \) , the slope of the graph of \( f \) is \( - 8 . \) (C) At \( x = 1 \) , the equation of the tangent line is \( y = - 8 x + 11 \) . (D) The tangent line is horizontal at \( x = \square \)
(Use a comma to separate answers as needed.)