(1) A certain cost function C(x) has the property that the average cost of producing 50 items is the same as the

Question

(1) A certain cost function C(x) has the property that the average cost of producing 50 items is the same as the

marginal cost of producing one more item when 50 are already made. Make a sketch of what this cost function's graph might look like. Can you give an example (a formula) of such a cost function? 

(2) Find all points (x; y) on the graph of y = cos x / 2+sin x where the tangent line is horizontal. 

(3) f 0 (x); f00(x); f(x) = 2x 3=2 ln(sin(5x))

Hello, can i get an answer for these 3 questions with explanations please?