. HW Score: 63.1%. 8.83 of 14 Question 12, 12.1.43 points (31 Points: 0 of 1 '6 Find all the values ofx where the tangent line is horizontal. f(X) = 2x'3 + 39x2 + 252x + 5 , using radicals as needed. Simplify your answer.) , K Clear all i answer an example Textbook 7 67 Clear