Long-run Supply Decision of the Perfectly Competitive Firm:

The long-run shutdown point for a perfectly competitive firm is the minimum point on its long-run average total cost (LAC) curve such as point C in Figure

In Figure, point C is the firm's shutdown point corresponding to price (P3) and output (Q3) below which the firm will not produce any output. The long-run supply curve of the firm is given by the long-run marginal cost curve (LMC) above point C (the minimum point on LAC)