If the qualification of a material as a linear n = 1 In the lower have of the inertia moment value corresponds to a rectangular area, therefore the equation (2.10).
If the properties of the material is a linear n = 1 will be reduced to match the In the moment of inertia of the rectangular area of the equation (2.10).
Considering the properties of material is linear n = 1 will make the In reduced to match the moment of inertia of the rectangular area, the following equation (2.10).