This document discusses different concepts in production economics including isocosts, least-cost input combinations, and returns to scale. It defines isocosts as cost curves that represent combinations of inputs that cost the same amount. Least-cost combinations are determined by superimposing isocost and isoquant curves to find points of tangency. Returns to scale refer to how output changes with proportional input changes. Constant returns mean output doubles with doubled inputs. Decreasing returns mean less than doubled output, while increasing returns mean more than doubled output.