Which advancement in mathematics contributed to improvements in algebra? the use of formulas to show data
the use of vertical and horizontal axes
the development of multiplication
the substitution of letters for unknown numbers

Suppose you are a freshmen in college and you have not declared a major. one reason you enrolled at your respective college was the school's vibrant social life. at the same time, you want to balance your academic life because you know that your grades will matter for graduate school or job applications. you decide to forgo partying for two hours to study for an upcoming economics exam. in your first semester's principles of economics class, you learn that the enjoyment you would have received from partying is an example of a(n)