7. (10 points) Let y = f(x) = 7 = 1x4+ 2x3 -5 (a) (2 points) On which intervals is f increasing or decreasing? Explain your reasoning. (b) (2 points) At what values of x does f have local maximum or minimum? Explain. (c) (2 points) On what interval is f concave up or concave down? Explain your reasoning