 the topic of isoquants. As we were discussing the various types of the terms or the phrases that we are going to utilize in the production process. So, what is called isoquant? Isoquant is basically the combination of the two things. One means iso, other is quant. Iso means same equal or the quant is the abbreviation of the quantity. So, any curve that provides the same level of the quantity or the same level of the output with various combination of the inputs, that curve or that map will be called isoquant. Or in other words, we can say various combinations of the capital and the labor that provide the same level of the output. Those are combinations when they are plotted on a curve or on a graph. The resultant graph or the curve it will be in a shape and that shape or that curve will be called isoquant. And now if we look at this isoquant, why are we explaining it? Actually, isoquant shows us various combinations available to the entrepreneur. Now, the meaning of these various combinations is that capital and labor or production functions that are present in it have the possible avenues to achieve the same output through different combinations. So, when the price of different inputs changes in the market or their non-availability or the price of a single one becomes favorable for them, then they can switch from one combination to another combination in all of these. But here all those combinations, when we draw them on one curve or join them, they appear in the shape of isoquant. Now, if we look at it, we say that suppose there is a form because this is an example. We are taking it from the same book which is recommended otherwise there can be the various combinations of various outputs. That is why I have drawn it in the shape of isoquant. It can be 60 pairs of jeans, 60 pairs of earrings, 60 pairs of socks. So, there can be any type of the output which we are producing from various combinations. Now, what are those combinations of? Capital and labor. And for that, we have drawn a table next to it. Now, these shows are pre-requisites for it. The combinations we are showing, during those combinations, the firm or the entrepreneur, their technical level of progress or technology is not changing. So, for all these combinations of capital and labor, the entrepreneur has to utilize the same level of the technology so that the technical progress aspect is zero. So, the isoquant curve that we have, when we bring the graph in a tabulated shape, we see that there are various combinations. If we look at the first combination, if we look at the A combination, we have taken three units of labor and 20 units of machine. And the output we have from these two is 60. Similarly, the next combination is B, in which we have increased the four units of labor, but in response to that, we have reduced the few units of the machine, and so on. So, it means there are the six types of the combinations which are giving us the same level of output, but the amounts of capital and labor are differing between them. And now, these six combinations, when we explain them in the form of this graph, because if we look at this graph here, the first A that we took for the units of machines, we have taken the combination. Now, we look at the next one. So, over this graph, we are reducing the input in the y-axis, and the input in the x-axis, i.e. in the form of labor, we are enhancing the amount of the input. So, in this form, we have these six combinations, and these six combinations, we are providing an equal level of output. Now, the arrow here is showing us that it might be the optimal level between these two. Now, what will be the optimal level? We will see this later. Or if we say that we are only looking at it from the technical aspect, but when we look at it from the economic aspect, then you know that the economic aspect is in which we include the cost. So, when we draw the curve of the firm's cost or its budget line, then its tendency tells us that out of these six combinations, which one combination will be the best or the optimal level of output for it? So, these six combinations can be optimal in various forms, because if its budget line is tangent to B, then B will be optimal. If C is tangent to T, then C will be tangent. And if we come to the T of D, then its D level will be optimal. But the graph on which all these combinations of capital and labor are expressing equal level of output, we can see this curve in the form of an isoquant. And in this isoquant, if we look at the inputs internally, then their diminishing rate of productivity is there. And because of this, and because of their internal difference, substitution is possible. So, when there is substitution between them, meaning the marginal rate of substitution between this capital and this labor, or the marginal rate of substitution between this capital and labor. So, looking at that, because it is diminishing, then this convects to a region. Now, if we look at this, then we have various aspects in front of us, that whenever we want to look at this, then we have law of diminishing marginal productivity related to input, which we have to take with our own concept. So, this technical law, we have law of diminishing marginal productivity, it asserts that this curve, whether it is inside, means board or bent, or if it is inward bending, then it will be in convex form. And similarly, because the forms, if one form increases the use of one factor, then we see that it can be reduced or increased, but whenever it will be reduced or increased, it has to be in this form that its output is constant. And in this, the switching of capital and labor, it will be showing its technical aspects, its various combinations. But we will not look at the diminishing marginal productivity. And that rate, or if we say that ratio, on which one factor is changing in this way with the other, that by adding one factor, we have to reduce the other, or by reducing one factor, we have to increase the other. So, this one, which we have ratio or rate, that will be called marginal rate of substitution. And in production, we call it marginal rate of technical substitution capital to labor.