Using Eq. 8.1.2 together with the values of D, and D2, we can evaluate D, for // in principle any value of n: (3 – 1){D2 +D1} = 2{1+0} (4 – 1){D3 +D2} = 3{2+1} (5 – 1){D4+D3} = 4{9+2} (6 – 1){Ds +D4} = 5{44+9} (7 – 1){D6+D5} = 6{265+44} (8 – 1){D7+D6} = 7{1854 +265} (9 – 1){D8 +D7} = 8{14833 +1854} (10 – 1){D9+Dg}= 9{133496 +14833} D3 2 D4 = 9. D5 = 44 D6 265 1 854 D7 D8 D9 D10 14 833 133 496 1 334 961 // It's strange that 1 334 961 // Is there a (convenient and compact) formula for D, that we can use to calculate // its values? = 10 × (133 496) + 1. Or is it? The sequence on P defined by S, = A × n! where A is any real number satisfies the recurrence equation (8.1.2). If n >= 3 then (n – 1){S„-2+Sn-1} = (n – 1){A(n – 2)! + A(n – 1)!} 3 (п — 1)4(п — 2){1+(n - 1)} %3D A(n - 1) (п — 2)n} = A x n! = Sn- // But will this "formula" apply when n = 1 or n = 2? // Does there exist a real number A such that D, // No, because if 0 = D1 = A(1!), then A must equal 0, // and A(n!) when n = 1 or n = 2? if 1 = D2 = A(2!), then A must equal ½. We can however use this formula to prove that D, is O(n!) by proving I| || || |||l || |

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Compute the values: D2 - 2D1, D3 - 3D2, D4 - 4D3, D5 - 5D4, …, D10 - 10D9, where the D’s are the derangements values described on P.335. What is the pattern?

Using Eq. 8.1.2 together with the values of D1 and D2, we can evaluate D, for
any value of n:
// in principle
D3
D4
D5
D6
D7
D8
D9
D10
(3 – 1){D2 +D1} = 2{1+0}
(4 – 1){D3+D2} = 3{2+1}
(5 – 1){D4+D3} = 4{9+2}
(6 – 1){D5+D4} = 5{44+9}
(7 – 1){D6+D5} = 6{265 +44}
(8 – 1){D7+D6} = 7{1854+265}
(9 – 1){D8 +D7} = 8{14833 +1854}
(10 – 1){D9+D3} = 9{133496 +14833}
2
9.
44
265
1 854
14 833
133 496
1 334 961
// It's strange that 1 334 961 =
// Is there a (convenient and compact) formula for D, that we can use to calculate
// its values?
10 x (133 496) + 1. Or is it?
The sequence on P defined by S,= A × n! where A is any real number satisfies
the recurrence equation (8.1.2). If n >= 3 then
(n – 1){Sn-2+Sn-1} = (n – 1){A(n – 2)! +A(n – 1)!}
= (n – 1)A(n – 2)!{1+[n – 1]}
= A(n – 1)(n – 2)!{n}
= Ax n!
= Sn.
// But will this "formula" apply when n = 1 or n =
// Does there exist a real number A such that Dn = A(n!) when n =
// No, because if 0 = D1 = A(1!), then A must equal 0,
// and
2?
1 or n = 2?
if 1 = D2 = A(2!), then A must equal ½.
We can however use this formula to prove that D, is O(n!) by proving
Theorem 8.1.1: For all n >= 2, (1/3)n! <= D, <= (1/2)n!
Consider the table of values
n
(1/3)n!
Dn
(1/2)n!
1
1/3
1/2
2/3
1
1 = 2/2
3
6/3 = 2
3 = 6/2
24/3 = 8
9.
12 = 24/2
120/3 = 40
44
60
= 120/2
6.
720/3 = 240
265
360 = 720/2
|| || || || || || ||
IL || || | || || || ||
ส์ร์ร์ ร์
Transcribed Image Text:Using Eq. 8.1.2 together with the values of D1 and D2, we can evaluate D, for any value of n: // in principle D3 D4 D5 D6 D7 D8 D9 D10 (3 – 1){D2 +D1} = 2{1+0} (4 – 1){D3+D2} = 3{2+1} (5 – 1){D4+D3} = 4{9+2} (6 – 1){D5+D4} = 5{44+9} (7 – 1){D6+D5} = 6{265 +44} (8 – 1){D7+D6} = 7{1854+265} (9 – 1){D8 +D7} = 8{14833 +1854} (10 – 1){D9+D3} = 9{133496 +14833} 2 9. 44 265 1 854 14 833 133 496 1 334 961 // It's strange that 1 334 961 = // Is there a (convenient and compact) formula for D, that we can use to calculate // its values? 10 x (133 496) + 1. Or is it? The sequence on P defined by S,= A × n! where A is any real number satisfies the recurrence equation (8.1.2). If n >= 3 then (n – 1){Sn-2+Sn-1} = (n – 1){A(n – 2)! +A(n – 1)!} = (n – 1)A(n – 2)!{1+[n – 1]} = A(n – 1)(n – 2)!{n} = Ax n! = Sn. // But will this "formula" apply when n = 1 or n = // Does there exist a real number A such that Dn = A(n!) when n = // No, because if 0 = D1 = A(1!), then A must equal 0, // and 2? 1 or n = 2? if 1 = D2 = A(2!), then A must equal ½. We can however use this formula to prove that D, is O(n!) by proving Theorem 8.1.1: For all n >= 2, (1/3)n! <= D, <= (1/2)n! Consider the table of values n (1/3)n! Dn (1/2)n! 1 1/3 1/2 2/3 1 1 = 2/2 3 6/3 = 2 3 = 6/2 24/3 = 8 9. 12 = 24/2 120/3 = 40 44 60 = 120/2 6. 720/3 = 240 265 360 = 720/2 || || || || || || || IL || || | || || || || ส์ร์ร์ ร์
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