prove-that-4-8-please-help-

Question Number 153006 by GalaxyBills last updated on 04/Sep/21

p r o v e t h a t

4!! = 8

p l e a s e h e l p

Commented by talminator2856791 last updated on 04/Sep/21

that is wrong .

n! = n \cdot (n - 1) \cdot (n - 2) \cdot \dots . . \cdot 2 \cdot 1

n!! = n! \cdot (n! - 1) \cdot (n! - 2) \cdot \dots . . \cdot

(n! - n) \cdot (n! - n - 1) \cdot \dots . . \cdot

(n! - 2 n) \cdot (n! - 2 n - 1) \cdot \dots . . \cdot

\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots .

.

.

n \cdot (n - 1) \cdot \dots . . \cdot 2 \cdot 1

4!! = 4! \cdot (4! - 1) \cdot \dots . . \cdot 2 \cdot 1

= 24 \cdot 23 \cdot \dots . . \cdot 2 \cdot 1

= 620 448 401 733 239 439 360 000

Commented by mr W last updated on 04/Sep/21

n!! \neq (n!)!

n!! = n \times (n - 2) \times (n - 4) \times \dots \times 2 o r 1

Commented by mr W last updated on 04/Sep/21

t h e r e i s n o w h y, j u s t k n o w i t i f y o u

{d i d n}^{'} t a l r e a d y k n o w .

Commented by talminator2856791 last updated on 04/Sep/21

why ?

Commented by talminator2856791 last updated on 04/Sep/21

then what is n!!! ?

Commented by mr W last updated on 04/Sep/21

Commented by mr W last updated on 04/Sep/21

n!!! = n (n - 3) (n - 6) \dots

Commented by Rasheed.Sindhi last updated on 04/Sep/21

I f m o d (n, 3) = 1 :

n!!! = n (n - 3) (n - 6) \dots \times 7 \times 4 \times 1

I f m o d (n, 3) = 2 :

n!!! = n (n - 3) (n - 6) \dots \times 8 \times 5 \times 2

I f m o d (n, 3) = 0 :

n!!! = n (n - 3) (n - 6) \dots \times 9 \times 6 \times 3

Answered by puissant last updated on 04/Sep/21

n!! = n (n - 2) (n - 4) \dots . \times 4 \times 2

4!! = 4 \times 2 = 8 .

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