Pí-sò͘

Tī sò͘-ha̍k, pí-sò͘ (rational number) sī 2 ê chéng-sò͘ ê pí (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:

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