True stress and strain are what are calculated by diving applied load by actual cross sectional area and change in length by length of specimen respectively. However, for engineering stress and strain, we use original area and original length. Generally, engineering Stress is always greater than the corresponding True Stress because the actual area increases due to Poisson's effect. Poisson's ratio is a measure of the Poisson effect, that describes the expansion of a material in directions perpendicular to the direction of compression. The value of Poisson's ratio is the negative of the ratio of transverse strain to axial strain.
In this case, he doesn't have a qualifying child. The reason is that his son doesn't live with him for more than half a tax year. Besides his incomes aren't enough to pay the tax exemption. His liability has to be removed because of his low wages.
