展开 (n-k-1)!(n-k)

解答

展开

(n - k - 1)! (n - k)

n (n - k - 1)! - k (n - k - 1)!

求解步骤

(n - k - 1)! (n - k)

使用分配律:

a (b - c) = ab - a c

a = (n - k - 1)!, b = n, c = k

= (n - k - 1)! n - (n - k - 1)! k

= n (n - k - 1)! - k (n - k - 1)!

e x p an d \frac{( - 2 t + 6 ) ( 2 t - 3 )}{t ^{2}}

e x p an d (4, 2, 3) x (- 2, 0, - 1)

e x p an d \frac{0.9 s}{( s - 0.1 ) ( x + 0.2 )}

e x p an d (e^{a} + e^{b}) \cdot e^{a}

e x p an d (- 0.8) (- 1.8) (- 2.6)