Which of the following curve in the input-output plane is an inverse ‘U’-shaped curve?

Both 2 and 3

The correct answer is Option 4: Both 2 and 3

The total product curve in the input-output plane is a positively sloped curve.

The MP curve and the AP curve both looks like an inverse ‘U’-shaped curve.

According to the law of variable proportions, the marginal product of an input initially rises and then after a certain level of employment, it starts falling. The MP curve therefore, looks like an inverse ‘U’-shaped curve.

For the first unit of the variable input, the MP and the AP are same. Now as we increase the amount of input, the MP rises. AP being the average of marginal products, also rises, but rises less than MP. Then, after a point, the MP starts falling. However, as long as the value of MP remains higher than the value of the AP, the AP continues to rise. Once MP has fallen sufficiently, its value becomes less than the AP and the AP also starts falling. So AP curve is also inverse ‘U’-shaped.