Algebra Glossary: R

radical: Symbol for the operation to find a square root.

radius: Distance from the center of a circle to its outer edge; half its diameter.

raised to the power of: Multiplying a base number the number of times indicated by the exponent. For example, 5 is being raised to the power of 3 in expression 53.

rational number: 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 1, such as 3 × 1/3 and 0.25 × 4. 2. Either one of the two numbers in a reciprocal. Example: 3 is the reciprocal of 1/3; and 1/3 is the reciprocal of 3.

rectangle: Four-sided plane figure with all right angles; its opposite sides are equal to one another in length.

reduce: Process in which a common factor of the numerator and denominator of a fraction is divided out, leaving an equivalent fraction.

relatively prime: Two numbers that have no factors in common other than the number 1.

remainder: 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. (Example: 3.3333… and 3.1787878…) Rounding off results in an estimated or approximate value.

right angle: 90-degree angle.

right triangle: Three-sided plane figure with a 90-degree angle (right angle).

root: Value that multiplied by itself a number of times results in the value or number wanted, such as 2 is the root of 4, because 2 multiplied by itself produces 4.

rounding off: Approximating the value to the nearest digit or decimal place, such as rounding 14.9 up to 15.