The 'law of diminishing returns' states that if the quantity of a single factor of production is increased incrementally even after attaining the optimal productivity and the other factors remain constant, the marginal productivity or output would tend to show a decline.
As per the question, the given description exemplify the 'law of diminishing returns' in economist's pattern because 'the incremental addition of marginal resources'would lead to bring a decline in the 'marginal benefit from this additional cost born by the firm' as after reaching an optimal level of production, the productivity tends to decline even after the additional expenditure on adding the marginal resources is made.
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