PERMS AND COMBS HELP (1 Viewer)

anne123123 · Apr 26, 2020

how do i solve this?

If 7 × 2nPn = 4 × 2n+1Pn,find n

Drdusk · Apr 26, 2020

anne123123 said:
how do i solve this?

If 7 × 2nPn = 4 × 2n+1Pn,find n

$\text{Use the fact that}\hspace{2mm} nPr = \dfrac{n!}{(n-r)!}$

$\text{Which gives you}\hspace{2mm}7\times \dfrac{(2n)!}{n!} = 4\times \dfrac{(2n+1)!}{(n+1)!}$

$\therefore 7\times \dfrac{(2n)!}{(2n+1)!} = 4\times \dfrac{n!}{(n+1)!}$

$\therefore 7\times \dfrac{1}{2n+1} = 4\times \dfrac{1}{n+1}\hspace{2mm}\text{(Trivial from here)}$

PERMS AND COMBS HELP (1 Viewer)

anne123123

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