Giải pt.. giúp vs này ^^

Question

1. $P_{x}A^{2}_{x}+ 72=6(A^{2}_{x}+2P_{x}$

2. $24(A^{2}_{x-1}- C^{x-4}_{x})= 23A^{4}_{x}$

câu 1 trước nha: x!*(x!/(x 2)!) 72=6(x!/(x-2)! 2x!)=>x!*(x-1)x 72=6(x(x-1) 2x!)=>x!(x-1)x 72=6x(x-1) 12x!=>x(x-1)(x!-6)=12(x!-6)=>x!-6=0 hoặc x(x-1)-12=0=>x=3 hoặc x=4 hoặc x=-3

@_@ *Mèo9119* @_@ · Answer 1 · 8/4/2016 10:48:34 PM

a) pt <=> $x!.\frac{x!}{(x-2)!}+72=6.\frac{x!}{(x-2)!}+12x!$

<=> $x!.x.(x-1)-12.x!-6.x.(x-1)+72=0$

<=> $x!(x^2-x-12)-6(x^2-x-12)=0$

Trả lời 04-08-16 10:48 PM

@_@ *Mèo9119* @_@
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@_@ *Mèo9119* @_@ · Answer 2 · 8/4/2016 10:43:57 PM

b) pt <=> $24(\frac{(x-1)!}{((x-1-2)!}-\frac{x!}{(x-4)!(x-x+4)!}=23.\frac{x!}{(x-4)!}$

<=> $24.(x-1)(x-2)-6.x(x-1)(x-2)(x-3)=23.x(x-1)(x-2)(x-3)$

Trả lời 04-08-16 10:43 PM

@_@ *Mèo9119* @_@
26 1

9K 266K

c lm hết rùi e – @_@ *Mèo9119* @_@ 04-08-16 10:49 PM

Cảm ơn chị nhaaa – ☻☻Tèo☻☻ 04-08-16 10:47 PM

chị làm luôn câu a đi ạ – EXO.NO1 04-08-16 10:44 PM

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