Assertion: triangle's cosine | /r/CapableOf | coincide with rational angle
Facets:
value: by niven's theorem
type: OTHER
Source sentences:
text: This is because integer sides imply three rational cosines by the law of cosines, and by Niven's theorem a rational cosine coincides with a rational angle if and only if the cosine equals 0, ±1/2, or ±1.