long run - allows for 2 (or more) variable inputs  

• diminishing marginal returns shown by drawing horizontal or vertical line through isoquant map
  • shows that each increased unit of capital or labor adds less and less to the total output

marginal rate of technical substitution (MRTS) - like MRS for consumers  

• amount of capital that can be decreased by an extra unit of labor, for a given output level
• MRTS = -DK/DL = MP_L/MP_K
  • MP = marginal product (partial derivatives of the production function w/ respect to either labor L or capital K)
• units of labor decrease the required capital less and less >> diminishing MRTS
  • isoquants are convex >> magnitude of the slope decreases (gets more flat) >> ratio of capital (vertical axis) to labor (horizontal) falls

• isoquant
• equivalent changes in labor lead to less and less change in capital >> diminishing MRTS