Question 5 of 8, Step 1 of 1 Correct 1 Use the definition of the derivative to find the derivative of the function f(x) = 5x2. Then find all x-values (if any) where the tangent line is horizontal. If the tangent line is horizontal for all x, write R for your answer. If the tangent line is never horizontal, write None for your answer. Answer Keypad Keyboard Shortc