The calculation of Gross Domestic Product (GDP) for the United States in 2009 can be approached through two primary methods: the expenditures approach and the income approach, both yielding the same GDP figure of $14,256 billion. This figure represents the total economic output of the country for that year.

In the expenditures approach, GDP is calculated by summing four key components: consumption (C), investment (I), government purchases (G), and net exports (NX). The formula can be expressed as:

$$ GDP = C + I + G + NX $$

Consumption is the largest component, reflecting household spending on goods and services. Investment includes business expenditures on capital goods, while government purchases account for government spending on goods and services. Net exports, which is calculated as exports minus imports, can be negative if imports exceed exports, indicating a trade deficit. In 2009, the U.S. had a trade deficit, contributing to a negative net exports figure.

On the other hand, the income approach calculates GDP by summing all incomes earned in the production of goods and services. This includes compensation of employees, rents, interest, proprietor income, corporate profits, and taxes on production and imports. The formula for total national income can be summarized as:

$$ National\ Income = Compensation\ of\ Employees + Rents + Interest + Proprietor\ Income + Corporate\ Profits + Taxes\ on\ Production\ and\ Imports $$

Adjustments are then made for foreign factor income, consumption of fixed capital, depreciation, and statistical discrepancies to ensure that the total aligns with the expenditures approach. The key takeaway is that expenditures equal income, reinforcing the interconnectedness of these two methods in measuring economic activity.

While both approaches are valid, the expenditures approach is often emphasized in economic studies, particularly focusing on the components of consumption, investment, government purchases, and net exports throughout the course of study.

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