radical: The symbol for the operation to find a square root.

raised to the power of: Multiplying a base number the number of times indicated by the exponent.

rational number: A quantity, positive or negative, that can be written as a fraction; its decimal equivalent terminates or repeats.

real number: Any rational or irrational number.

reciprocal; multiplicative inverse: 1. Two numbers whose product is always one. 2. Either one of the two numbers in a reciprocal.

reduce: To divide out a common factor of the numerator and denominator of a fraction, leaving an equivalent fraction.

relatively prime: The condition of two numbers that have no factors in common other than the number one.

remainder: A value that is left over when one number is divided by another.

repeating decimal; recurring decimal: A decimal in which, beyond a certain point, a digit or set of digits repeats indefinitely.

root: A value that, multiplied by itself a number of times, results in the value or number wanted.

rounding: Approximating a value to the nearest digit or decimal place.