Please help!

Use the definition of derivative, prove that d = dx (V3 - 2x) V3 - 2x [6] Let f(x) = 3x4 - 8x3 - 90x2. (i) Find the open intervals on which f is (a) increasing (b) decreasing (c) concave up (d) concave down. [4] (ii) Find the coordinates of all the local maximum and local minimum points of f. Co (iii ) Find the coordinates of all the inflection points of f. [2] (iv) Use the information in (i) to (iii) to sketch the graph of f