Figure 6.4 The Marginal Rate of Technical Substitution
The negative slope of the isoquant is the marginal rate of technical substitution of labor L for capital K. At point A, the marginal product of labor is high relative to the marginal product of capital, and a relatively small decrease in labor would require a large quantity of capital to hold output constant. At point B, the marginal product of labor is low relative to the marginal product of capital, and a relatively small decrease in capital would require a large quantity of labor to hold output constant.