which of the following curves is not U shaped

Analyze the question: We need the cost curve that does NOT have a U shape.

Concept: Because of the law of diminishing returns (variable proportions), short-run cost curves behave as follows:

• Marginal cost (MC): falls at first, reaches a minimum, then rises, so it is U-shaped.
• Average variable cost (AVC): falls, reaches a minimum, then rises, so it is U-shaped.
• Average total cost (ATC): ATC = AFC + AVC. It is also U-shaped, with its minimum point lying to the right of the AVC minimum.
• Average fixed cost (AFC): AFC = TFC ÷ Q. Total fixed cost stays constant, so as output rises, AFC keeps falling. It slopes downward throughout and approaches the horizontal axis without ever touching it. This makes it a rectangular hyperbola, not U-shaped.

Solution:

• A. MC: U-shaped
• B. AFC: continuously downward-sloping, not U-shaped
• C. ATC: U-shaped
• D. AVC: U-shaped

Answer: B. Average fixed cost curve.

Tip: Remember that "fixed" costs are spread over more units as output grows, so AFC only falls. Any curve that includes variable costs (MC, AVC, ATC) eventually rises because of diminishing returns, which gives it a U shape.