Profit is maximized at the output at which marginal revenue exceeds marginal cost by the greatest margin. Total profit is represented by the vertical distance between a total revenue curve and a total cost curve.
The denominator in each term of the series is a square number, but neither nor are squares. So none of (1), (2), and (4) can be correct. The answer must be (3).
nor 
are squares. So none of (1), (2), and (4) can be correct. The answer must be (3).