The region inside of the two ridge lines in the isoquantdiagram
is where the marginal product of the two inputs is negative and
that of the other positive.
Isoquant is a curve along which the output will be same.
When a firm produces a particular amount of a commodity by
applying different mixture of labour and capital, when this details
is drawn on a graph , we acquire an isoquant.
The marginal product of a factor may be negative if the
quantity used is too large. The area of rational operation drawn by
showing two lines from the beginning surround those parts of
isoquant has a positive marginal product and those lines are called
ridge lines.
Negative marginal product are visible in that part of the
isoquant which has a positive slope.