Question: how to calculate the marginal product of capital?
Answer: Dividing this quantity by ∆K gives the change in the production per unit change in capital, ∆Q ∆K = f(L, K + ∆K) − f(L, K) ∆K . ∂Q ∂L = aALa−1 Kb = aQ K . Thus, for the Cobb-Douglas production function, the marginal product of capital (resp. labor) is a constant times the average product of capital (resp.