化简 (n!)/(3!(n-3)!)

解答

化简

\frac{n !}{3 ! ( n - 3 ) !}

\frac{n ( n - 1 ) ( n - 2 )}{6}

求解步骤

\frac{n !}{3 ! ( n - 3 ) !}

消去因子:

\frac{n !}{( n - m ) !} = n \cdot (n - 1) \dots (n - m + 1), n > m

\frac{n !}{( n - 3 ) !} = n (n - 1) (n - 2)

= \frac{n ( n - 1 ) ( n - 2 )}{3 !}

3! = 6

= \frac{n ( n - 1 ) ( n - 2 )}{6}

\frac{y + 5}{2} - \frac{y - 2}{4} = \frac{y + 7}{3} + 1

- \frac{1}{2} x \leq - \frac{3}{4} + \frac{2}{5} x

(x + 7)^{2} = 28

s im pl i f y 12 8^{\frac{3}{7}}

f a c t or x^{2} + 2 x y + y^{2}