展开 (n-r)!(n+1-r)

解答

展开

(n - r)! (n + 1 - r)

n (n - r)! + (n - r)! - r (n - r)!

求解步骤

(n - r)! (n + 1 - r)

打开括号

= (n - r)! n + (n - r)! \cdot 1 + (n - r)! (- r)

使用加减运算法则

+ (- a) = - a

= n (n - r)! + 1 \cdot (n - r)! - r (n - r)!

乘以:

1 \cdot (n - r)! = (n - r)!

= n (n - r)! + (n - r)! - r (n - r)!

e x p an d \frac{3 x - 2}{x ( x - 2 ) ( x + 1 ) ( x + 3 )}

e x p an d \frac{- x + 1}{5 ( x + 2 )}

e x p an d 2^{x (x - 1)}

e x p an d \frac{2}{s ( s ^{2} + 2 s + 2 )}

e x p an d \frac{( y + 1 ) ^{2}}{2}