The document discusses the different shapes a production possibilities frontier (PPF) can take depending on the production function of the goods. A PPF will be linear if production exhibits constant returns to scale (CRS), convex if diminishing returns to scale (DRS) where later units are more costly, and concave if increasing returns to scale (IRS).

1. Shapes of PPF
PPF when production function of
goods produced exhibits CRS. Often
used when there is only one factor of
production
PPF when production function of
goods produced exhibits DRS. The
cost of producing additional units
gradually increases, the last unit being
most costly
PPF when production function of
goods produced exhibits IRS.