Explain the difference between main and variable capital

Constant capital (c), is a concept created by Karl Marx and used in Marxian political economy. It refers to one of the forms of capital invested in production, which contrasts with variable capital (v). The distinction between constant and variable refers to an aspect of the economic role of factors of production in creating a new value.
Constant capital includes the outlay of money on (1) fixed assets, i.e. plant, machinery, landand buildings, (2) raw materials and ancillary operating expenses (including external services purchased), and (3) certain faux frais of production (incidental expenses). Variable capital by contrast refers to the capital outlay on labour costs insofar as they represent workers' earnings.
The concept of constant vs. variable capital contrasts with that of fixed vs. circulating capital (used not only by Marx but by David Ricardo and other classical economists). The latter distinction corresponds to the very common distinction in economics, between fixed inputs (and costs) and variable inputs (and costs). It distinguishes inputs from the point of view of their user (the capitalist), in terms of the degree of flexibility that the user has in using them.
On the other hand, constant capital refers to the non-human inputs into production, while variable capital refers to the human input (the hiring of labor power to do labor).

24)Explain the formula of capital circulation
Circulation of Capital

the movement of automatically growing value in production and distribution, during which the capital assumes three functional forms (monetary, productive, and commodity) and passes through three stages. At the end of the process, the capital returns to its initial form.
The first stage of the movement of industrial capital is the conversion of monetary capital (M) into productive capital, that is, the purchase of commodities (C); these commodities are composed of the means of production (MP) and labor (L). This stage is expressed by the formula

Capital passes through the first stage in the sphere of circulation: the purchase of a specific commodity, labor, converts money into capital that is returned to its owner in an amount exceeding the initial capital value by the magnitude of the surplus value. Thus, monetary capital expresses the relations between two classes in bourgeois society: the workers, who are deprived of the means of production and forced to sell their labor, and the capitalists, the owners of the means of production.
The condition for the conversion of money into capital is the existence of a specific commodity, labor, in the market. In the first stage of the circulation of capital, no growth in value occurs. The second stage of the circulation of capital, the conversion of productive capital into commodity capital, takes place in the production sphere and is expressed by the formula … P …, where P standsfortheprocessofproduction. This stage is characterized by growth in capital value. The function of capital in this form is to produce value and surplus value. The means of production become the material carrier of constant capital, whereas labor is the carrier of variable capital. The value of the commodity newly created in the production process already includes surplus value. The third stage is the conversion of commodity capital into monetary capital. It is expressed by the formula C’ — M’ and takes place in the distribution sphere. The function of commodity capital is the process of selling, that is, conversion of the produced value and surplus value from the commodity form into the monetary form. With the conversion of commodity capital into the monetary form, the circulation of capital is completed; capital begins a new circulation in its initial form, monetary capital.

25)Explain the meaning of investment from economic and finance point of view
In a broad sense, all investments are alike: You spend money or commit resources now in the hope of earning a return later. Go just a bit deeper, however, and you see significant differences in the way investments are expected to pay off. Economists draw a key distinction between economic investments, which generate wealth through economic activity, and financial investments, which generate wealth primarily through finance -- the manipulation of money.
Economic Investments
Management professors Krishnamurthy Nagarajan and G. Jayabal define economic investment as investment that increases the "capital stock" of society -- in other words, it increases production capacity. Economic investment allows companies to provide more or better products and services. New buildings, equipment and vehicles obviously represent economic investment, but so can spending on education and health care. Those things improve "human capital," making workers more productive.
Financial Investments
A share of stock is a quintessential example of a financial investment. If you're like most investors, when you buy a share of stock, you're not planning to "do something" with it. You're not going to use it to increase production of anything or improve the quality of any products. You buy it with the hope that it will increase in value so when you sell it, you'll make money. In the meantime, you'd like to collect dividends -- regular payments from the company that issued the stock. Nothing new is directly created from a financial investment; rather, as Michael Douglas Gilbert writes in "America in the Economic World," a financial investment simply represents an asset changing hands. Other examples can include bonds; gold and other precious metals, when purchased as a store of value rather than for industrial use; money earning interest in a savings account; and real estate that you don't develop or improve.