Let f(x)=x+3x - 189x+6. Use the definition of a derivative or the derivative rules to find f'(x). f'(x) = Use the definition of a derivative or the derivative rules to find f"(x). f"(x)= On what interval is f increasing (do not include the endpoints in the interval)? Interval on which f is increasing: On what interval is f decreasing (do not include the endpoints in the interval)? Interval on which f is decreasing: On what interval is f concave down (do not include the endpoints in the interval)? Interval of downward concavity: On what interval is f concave up (do not include the endpoints in the interval)? Interval of upward concavity: