cricket farming for profit Historically, the concept of income has first appeared in economics. Adam Smith, in the wealth of nations, defined income as "the amount of consumption that is not eroded by capital", and saw it as an increase in wealth. Later, most economists inherited and developed this view. 1890, ai (Alfred Marshall Maarshell) in its "the principles of economics," the Adam Smith's "wealth increase" enterprise, introduced the concept of earnings, is proposed to distinguish the entity capital and value-added benefits of economic benefits. Diversification of securities, the establishment of a scientific and effective portfolio of securities; In theoretical economics, investment means buying (and therefore producing) capital goods - not being consumed but being used in future production. Examples include building railroads, or factories, cleaning the land, or allowing yourself to go to college. Strictly speaking, investment in formula GDP= C + I + G + NX is also part of gross domestic product. In that respect, the function of investment is divided into non-residential investments (such as factories, machinery, etc.) and residential investment (new homes). The correlation between I = (Y, I) is known to have a close relationship with income and interest rates. Higher incomes would boost higher investment, but higher interest rates would discourage investment because it would be more expensive to borrow. Even if companies choose to use their own funds to invest, interest rates represent the opportunity cost of investing in those funds rather than the interest that will lend out.