정답
$\binom{n}{r} = \frac{n!}{r!(n - r)!}$.
해설
In contrast, permutations $_nP_r = \frac{n!}{(n - r)!}$ account for ordering. A key property is symmetry: $\binom{n}{r} = \binom{n}{n - r}$.
홈 / 라이브러리 / CSAT (Suneung) essentials: original practice / AI 플래시카드
What is the formula for the number of combinations $\binom{n}{r}$ (or $_nC_r$) of choosing $r$ items from $n$ distinct objects without regard to order?
덱 'CSAT (Suneung) essentials: original practice'의 플래시카드.