Pí-sò͘

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sò͘-ha̍k, pí-sò͘ (rational number) sī 2 ê chéng-sò͘ ê (ratio) ia̍h siong, tiāⁿ siá chò a/b, b m̄ sī 0. Phó͘-thong-sî-á koàn-sì kā pí-sò͘ kiò chò hun-sò͘ (fraction), mā ū lâng kā hō chò iú-lí-sò͘.

Ta̍k ê pí-sò͘ ê siá-hoat bô chīn-pōng, khó-pí kóng 3/6 = 2/4 = 1/2. Nā a ham b bô kong-ke ê iok-sò͘ (divisor) ê sî, sī siōng kán-tan ê hêng. Hun-bú sī chiàⁿ--ê, m̄ sī 0 ê pí-sò͘ kan-taⁿ ū 1 ê chit khoán siōng kán-tan ê hêng, hō chò siōng-kán hun-sò͘ (irreducible fraction).

Pí-sò͘ ê cha̍p-chìn-ūi piáu-sī (decimal representation) siōng boé tiāⁿ-tio̍h ē sûn-khoân. Khêng-si̍t, ēng phēng 1 toā ê chéng-sò͘ chò ki-té (base) lóng ē án-ni. Tian-tò-pái, chún-nā 1 ê sò͘-ba̍k ēng bó͘-mih ki-té piáu-sī ê sî ē sûn-khoân, án-ne só͘-ū ê ki-té lóng ē sûn-khoân, jî-chhiáⁿ chit ê sò͘-ba̍k tiāⁿ-tio̍h sī pí-sò͘.

M̄ sī pí-sò͘ ê si̍t-sò͘ hō chò hui-pí-sò͘ (irrational number).

Só͘-ū ê pí-sò͘ ha̍p--khí-lâi ê chi̍p-ha̍p sī 1 ê thé, koàn-sì siá chò Q ia̍h \mathbb{Q}. Ēng chi̍p-ha̍p khí-chō hû-hō (set-builder notation) lâi siá, \mathbb{Q} ê tēng-gī tō sī:

\mathbb{Q} = \left\{\frac{m}{n} : m \in \mathbb{Z}, n \in \mathbb{Z}, n \ne 0 \right\}