(A) TFC = AFC × quantity -> Since AFC = TFC/quantity, multiplying both sides by quantity gives TFC = AFC × quantity. This is correct.
(B) LRMC = (TC at qn units) – (TC at qn−1 units) -> Marginal cost is defined as the change in total cost when output increases by one unit. This correctly represents LRMC.
(C) TC = TVC × TFC -> The correct relationship is TC = TVC + TFC (addition, not multiplication). Total cost equals the sum of total variable cost and total fixed cost. This is incorrect.
(D) LRAC = TC/q -> Long Run Average Cost is calculated by dividing Total Cost by quantity. This is correct.
Hence, Option 1: (A), (B) and (D) only -> Equations (A), (B), and (D) follow the correct cost relationships in economics. Equation (C) is incorrect because total cost is the sum (not product) of total variable cost and total fixed cost. The fundamental cost relationship is additive: TC = TVC + TFC. -> correct