can the marginal product of capital be negative
Marginal product In the "law" of diminishing marginal returns, the marginal product initially increases when more of an input (say labor) is employed, keeping the other input (say capital) constant. Here, labor is the variable input and capital is the fixed input (in a hypothetical two-inputs model). As more and more of variable input (labor) is employed, marginal product starts to fall. Finally, after a certain point, the marginal product becomes negative, implying that the additional unit of labor has decreased the output, rather than increasing it. The reason behind this is the diminishing marginal productivity of labor.
Share capital In a strict accounting sense, share capital is the nominal value of issued shares (that is, the sum of their par values, as indicated on share certificates). If the allocation price of shares is greater than their par value, e.g. as in a rights issue, the shares are said to be sold at a premium (variously called share premium, additional paid-in capital or paid-in capital in excess of par). Commonly, the share capital is the total of the aforementioned nominal share capital and the premium share capital. Conversely, when shares are issued below par, they are said to be issued at a discount or part-paid.