問幾條數~求解☆★☆★☆★

wl00341512

1.
    (n+6)!
    ---------
    (n+4)!


2. nP3

3.nC2

4.n+1C3

yukating

1. (n+6)!/(n+4)!
= (n+6)(n+5)(n+4)!/(n+4)!
= (n+6)(n+5)
2. 無教.
3. ⁿC₂
= n(n-1) / (1x2)
= 1/2(n)(n-1)
4. ⁿ⁺¹C₃
= ⁿC₃ + ⁿC₂
= n!/[6(n-3)!] + n!/[2(n-2)!]
= n!/[2x3(n-3)! + n!/[2(n-2)(n-3)!]
= {n!/[2(n-3)!]}[1/3+1/(n-2)]
= {[n(n-1)(n-2)]/2}[1/3+1/(n-2)]
= {[n(n-1)(n-2)]/2}[n+1/3(n-2)]
= [(n+1)(n)(n-1)]/6

[S]【YU】

2. nP3 = n(n-1)(n-2)

3.nC2 = n(n-1)/(1x2)

4.n+1C3 = (n+1)n(n-1)/(1x2x3)

wl00341512

1. (n+6)!/(n+4)!
= (n+6)(n+5)(n+4)!/(n+4)!
= (n+6)(n+5)
2. 無教.
3. nC2
= n(n-1) / (1x2)
= 1/2(n)(n-1)
4. n+1C3
= nC3 + nC2
= n!/[6(n-3)!] + n!/[2(n-2)!]
= n!/[2x3(n-3)! + n!/[2(n-2)(n-3)!]
=  ...
yukating 發表於 20-10-2009 22:34

3同我份答案有小小唔同
多謝你解答

2. nP3 = n(n-1)(n-2)

3.nC2 = n(n-1)/(1x2)

4.n+1C3 = (n+1)n(n-1)/(1x2x3)
[S]【YU】 發表於 20-10-2009 22:44

我想要條式..唔該

[S]【YU】

呢個係Combination 基本既運算,無式可言

正如小數轉百分比 0.1 = 0.1 x 100% , 乜仲有式既咩?

e.g.
50C2 = (50x49)/(1x2)
100C5 = (100x99x98x97x96)/(1x2x3x4x5)

pllo19940612

係咪M1/M2嫁= =
未見過...