b. i. Suppose f is continous on [a, b] and differentiable on (a, b). Prove that if f(x) >0 for every x e(a, b) then f increases throughout (a, b) (4 marks) ii. Find the intervals on which f(x)=2+x-x2 increases and decreases. Hence, sketch the graph of this function. (4 marks)​