Two inputs are said to complementary if their cross-partial derivative D2xixjf(x) is positive, since this means that

Question:

Two inputs are said to complementary if their cross-partial derivative D2xixjf(x) is positive, since this means that increasing the quantity of one input increases the marginal productivity of the other. Show that if a production function of two inputs is linearly homogeneous and quasi concave, then the inputs are complementary.