Why are the investment function, the government spending function, and the export function all drawn as flat lines?

Investment function in economics refers to the relationship between the total production level of an economy (Gross Domestic Product) and the amount of money invested within that economy by the private sector. This investment can be money spent on buying capital goods or building infrastructure. The investment function can be mathematically represented as: \( I = I_0 \) Here, \(I\) represents the total amount of investment and \(I_0\) is a constant showing the autonomous investment, which is independent of the income level.

Government spending function refers to the relationship between the total production level of an economy (Gross Domestic Product) and the amount of money spent by the government through its various activities like purchasing goods and services, funding infrastructure projects and social welfare programs. The government spending function can be represented as: \( G = G_0 \) Here, \(G\) represents the total amount of government spending and \(G_0\) is a constant, representing the autonomous government spending independent of the income level.

Export function in economics refers to the relationship between the total production level (Gross Domestic Product) of an economy and the amount of goods and services that are exported to other countries. The export function can be mathematically represented as: \( X = X_0 \) Here, \(X\) represents the total amount of exports and \(X_0\) is a constant, representing the autonomous export independent of the income level.

Now that we have introduced the investment function, government spending function, and export function, we can analyze why all these three functions are represented as flat lines in the economic graph. Investment, government spending, and export functions are graphed as flat lines because they are all assumed to be autonomous, i.e., independent of the income level of an economy. In simple terms, no matter how much the Gross Domestic Product of an economy increases or decreases, the investment, government spending, and export functions are assumed to remain constant. So, they do not vary with the changes in income levels. As we saw above in their respective equations, \( I = I_0 \), \( G = G_0 \), and \( X = X_0 \), all these functions have no variable component dependent on the income level, and they have the same constant values across the entire range of income levels. In graphical terms, this means that they are represented as flat, horizontal lines parallel to the x-axis (income level axis) where the y-coordinate represents the respective constant values \(I_0\), \(G_0\), and \(X_0\).