Unobtrusive measures: a. A process in which numbers are assigned according to rules of correspondence between definitions and observations. b. The study of physical traces, archives, and observation without participation. c. The process of figuring out how to measure concepts using empirical evidence. d. The challenge of collecting data without it being affected by certain external obstructions.

1- what do you think the product of a nonzero rational number and an irrational number is? is it rational or irrational? make use of variables, the closure property of integers, and possibly a proof by contradiction to prove your hypothesis.2- why do we have to specify that the rational number must be nonzero when we determine what the product of a nonzero rational number and an irrational number is? if the rational number were 0, would it give us the same result we found in the first question?