Why is it true that all irrational numbers are non-terminating/non-repeating decimals?

Deborah Proctor

Deborah Proctor

Answered question

2022-10-28

Why is it true that all irrational numbers are non-terminating/non-repeating decimals?

Answer & Explanation

jbaekk7q

jbaekk7q

Beginner2022-10-29Added 18 answers

The definition: a number is irrational if and only if it's not rational, i.e. it can't be expressed as a ratio of two integers.
If x has a repeating decimal expansion (this includes terminating decimal expansions), then x is rational.
Proof: If x has a repeating decimal expansion, then it can always be written in the following form:
Let c , b be non-negative integers and a i { 0 , 1 , 2 , , 9 } and t is the number of digits of b.
x = c . b a 1 a 2 a k a 1 a 2 a k a 1 a 2 ¯
10 t x = c b . a 1 a 2 a k a 2 a 2 a k a 1 a 2 ¯
10 k t x = c b a 1 a 2 a k . a 1 a 2 a k a 1 a 2 ¯
10 k t x 10 t x = c b a 1 a 2 a k ¯ c b ¯
x = c b a 1 a 2 a k ¯ c b ¯ 10 k t 10 t

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