Question: United Widgets plc has a production function which displays increasing returns in the output range from zero to X1, constant returns from X1 to X2, and diminishing returns thereafter. What is the shape of the firm's long-run total cost curve? What is the relationship between long-run average and long-run marginal cost at levels of output between X1 and X2? Draw the long-run average and marginal cost curves for United Widgets.