How did the achievements of the gupta empire make higher-level mathematics possible? a. they invented writing materials that allowed for the easy correction of mistakes. b. they developed the idea of multiplication as repeated addition. c. they discovered the number pi and were the first to calculate the area of a circle. d. they invented the numeral zero and the decimal system of numbers.

Match the item to the definition: indirect correlation, correlational research, correlational research, covary, pearson correlation coefficient, pearson correlation coefficient, direct correlation a. used to describe the relationship between two or more naturally occurring variables b. determines whether scores on the two variables covary c. whether two variables vary or change together d. denoted by the symbol "r" e. provides information about the sign (direction) and magnitude(strength) of the linear relationship. f. when the correlation is positiveg. when the correlation is negative