Rational numbers and recurring decimals
Terminating or eventually recurring decimals represent exactly the rational numbers.
Key knowledge
A real number is rational exactly when it has a decimal expansion that terminates or eventually repeats. For a reduced fraction a/b with positive b, termination occurs exactly when b has no prime factors except 2 and 5.
Values and equations
b = 2^u·5^v ⇔ a/b has a terminating base-ten expansion, when gcd(|a|,b)=1 and b>0
- a, b
- Integers in a reduced fraction
- u, v
- Nonnegative integers
Conditions and scope
- Use base ten and reduce the fraction before testing its denominator; b=1 is allowed.
- A nonzero terminating value also has a recurring-nine representation; a finite observed prefix cannot establish eventual repetition.
Only these mathematical portions; no independent proof certification.
Sources · 1
References
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Evidence and review
Checked the stated rational numbers and recurring decimals and restrictions against the listed primary sections; exact inspected boundaries are in the author receipt.
2026-10-10 · Independent Physics and Measurement reference editor (AI editorial bounded review). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
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- foundation-math-rational-decimals
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- foundations-refresh.1
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