Implicit costs are the opportunity costs of using resources already owned by the firm.
Normal profit is one example of an implicit cost.
A firm is a price taker when its output decision has no effect on market price . The demand curve faced by the price-taking firm is perfectly elastic at the market price. A firm that has some degree of price-setting power is a price searcher . The demand curve faced by the price-searching firm is downward sloping. MR declines as output increases since the firm faces a downward sloping demand curve.