Answer:
The primary difference between those two concepts is focus that each term has. The first one focus on the relationship between the level of production and the level of return. While the second one focus on the relationship between the level of production and the amount of factors used for that production.
Step-by-step explanation:
One the one hand, the law of diminishing marginal returns is a concept known in the microeconomics theory due to the fact that it establishes the relationship between the productivity and the income for every aspect of it. Meaning that, when the productivity increases because of the increase of only one factor of production then the income will start to slowly decrease, confirming that when only one factor is increased the production will start to be incomplete and the return will decrease for that.
On the other hand, the law of diminishing marginal rate of technical substitution indicates the relationship between the level of output and the different factor used to produce. Meaning that, it shows how to keep the level of output the same while making changes in the amount of factors used.