Math CentralQuandaries & Queries


Question from Juli, a student:

My teacher recently put my math class to the test...

We were discussing repeating fractions and she asked us to find out what the bar over a repeating decimal is called. I found out it was called the vinculum. But she also said to find out what the number under the vinculum was called. I can't seem to find it anywhere.

Hi Juli,

I looked in Earliest Known Uses of Some of the Words of Mathematics and read through the words beginning with R as I thought the word you are looking for would be related to the word repeat. I found

REPETEND appears in 1714 in A new and compleat treatise of the doctrine of fractions, vulgar and decimal by Samuel Cunn: "The Figure or Figures continually circulating, may be called a Repetend."

I then looked up repetend in the Oxford English Dictionary and found the first definition under the noun repetend to be

1. Arith. The recurring figure or figures in an interminate decimal fraction.

The OED also says repetend can be used as an adjective but says it is rarely used. The meaning of the adjective repetend is

That is to be repeated.

I think your teacher is looking for the word repetend.


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