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!Ignotum/Formulae/Seri

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# Maths > Series
nth term=a+(n-1)d
For an arithmetic progression, eg 1 3 5 7
9 etc.
a=starting number (eg 1)
d=common difference (eg 2)

S<n>=(n/2)(2a+(n-1)d)
For an arithmetic progression, eg 1 3 5 7
9 etc.
S<n>=sum of the numbers up to term n.
a=starting number (eg 1)
d=common difference (eg 2)
nth term=ar^(n-1)
For a geometric progression, eg 1 2 4 8 16
a=starting number (eg 1)
r=common ratio (eg 2)


S<n>=a(1-r^n)/(1-r)
For a geometric progression, eg 1 2 4 8 16
S<n>=sum of the numbers up to term n.
a=starting number (eg 1)
r=common ratio (eg 2)

S<i>=a/(1-r)
For a geometric progression, when |r|<1,
eg 1 1/2 1/4 1/8 1/16
S<i>=sum of terms to infinity
a=starting number (eg 1)
r=common ratio (eg �)
e=(1/0!)+(1/1!)+(1/2!)+(1/3!)+(1/4!)...
This is one way of calculating e (2.718),
where a! is the factorial of a:
a(a-1)(a-2)(a-3).. until a-n=1
Note: 0!=1



















































































































00000000  23 20 4d 61 74 68 73 20  3e 20 53 65 72 69 65 73  |# Maths > Series|
00000010  0a 6e 74 68 20 74 65 72  6d 3d 61 2b 28 6e 2d 31  |.nth term=a+(n-1|
00000020  29 64 0a 46 6f 72 20 61  6e 20 61 72 69 74 68 6d  |)d.For an arithm|
00000030  65 74 69 63 20 70 72 6f  67 72 65 73 73 69 6f 6e  |etic progression|
00000040  2c 20 65 67 20 31 20 33  20 35 20 37 0a 39 20 65  |, eg 1 3 5 7.9 e|
00000050  74 63 2e 0a 61 3d 73 74  61 72 74 69 6e 67 20 6e  |tc..a=starting n|
00000060  75 6d 62 65 72 20 28 65  67 20 31 29 0a 64 3d 63  |umber (eg 1).d=c|
00000070  6f 6d 6d 6f 6e 20 64 69  66 66 65 72 65 6e 63 65  |ommon difference|
00000080  20 28 65 67 20 32 29 0a  0a 53 3c 6e 3e 3d 28 6e  | (eg 2)..S<n>=(n|
00000090  2f 32 29 28 32 61 2b 28  6e 2d 31 29 64 29 0a 46  |/2)(2a+(n-1)d).F|
000000a0  6f 72 20 61 6e 20 61 72  69 74 68 6d 65 74 69 63  |or an arithmetic|
000000b0  20 70 72 6f 67 72 65 73  73 69 6f 6e 2c 20 65 67  | progression, eg|
000000c0  20 31 20 33 20 35 20 37  0a 39 20 65 74 63 2e 0a  | 1 3 5 7.9 etc..|
000000d0  53 3c 6e 3e 3d 73 75 6d  20 6f 66 20 74 68 65 20  |S<n>=sum of the |
000000e0  6e 75 6d 62 65 72 73 20  75 70 20 74 6f 20 74 65  |numbers up to te|
000000f0  72 6d 20 6e 2e 0a 61 3d  73 74 61 72 74 69 6e 67  |rm n..a=starting|
00000100  20 6e 75 6d 62 65 72 20  28 65 67 20 31 29 0a 64  | number (eg 1).d|
00000110  3d 63 6f 6d 6d 6f 6e 20  64 69 66 66 65 72 65 6e  |=common differen|
00000120  63 65 20 28 65 67 20 32  29 0a 6e 74 68 20 74 65  |ce (eg 2).nth te|
00000130  72 6d 3d 61 72 5e 28 6e  2d 31 29 0a 46 6f 72 20  |rm=ar^(n-1).For |
00000140  61 20 67 65 6f 6d 65 74  72 69 63 20 70 72 6f 67  |a geometric prog|
00000150  72 65 73 73 69 6f 6e 2c  20 65 67 20 31 20 32 20  |ression, eg 1 2 |
00000160  34 20 38 20 31 36 0a 61  3d 73 74 61 72 74 69 6e  |4 8 16.a=startin|
00000170  67 20 6e 75 6d 62 65 72  20 28 65 67 20 31 29 0a  |g number (eg 1).|
00000180  72 3d 63 6f 6d 6d 6f 6e  20 72 61 74 69 6f 20 28  |r=common ratio (|
00000190  65 67 20 32 29 0a 0a 0a  53 3c 6e 3e 3d 61 28 31  |eg 2)...S<n>=a(1|
000001a0  2d 72 5e 6e 29 2f 28 31  2d 72 29 0a 46 6f 72 20  |-r^n)/(1-r).For |
000001b0  61 20 67 65 6f 6d 65 74  72 69 63 20 70 72 6f 67  |a geometric prog|
000001c0  72 65 73 73 69 6f 6e 2c  20 65 67 20 31 20 32 20  |ression, eg 1 2 |
000001d0  34 20 38 20 31 36 0a 53  3c 6e 3e 3d 73 75 6d 20  |4 8 16.S<n>=sum |
000001e0  6f 66 20 74 68 65 20 6e  75 6d 62 65 72 73 20 75  |of the numbers u|
000001f0  70 20 74 6f 20 74 65 72  6d 20 6e 2e 0a 61 3d 73  |p to term n..a=s|
00000200  74 61 72 74 69 6e 67 20  6e 75 6d 62 65 72 20 28  |tarting number (|
00000210  65 67 20 31 29 0a 72 3d  63 6f 6d 6d 6f 6e 20 72  |eg 1).r=common r|
00000220  61 74 69 6f 20 28 65 67  20 32 29 0a 0a 53 3c 69  |atio (eg 2)..S<i|
00000230  3e 3d 61 2f 28 31 2d 72  29 0a 46 6f 72 20 61 20  |>=a/(1-r).For a |
00000240  67 65 6f 6d 65 74 72 69  63 20 70 72 6f 67 72 65  |geometric progre|
00000250  73 73 69 6f 6e 2c 20 77  68 65 6e 20 7c 72 7c 3c  |ssion, when |r|<|
00000260  31 2c 0a 65 67 20 31 20  31 2f 32 20 31 2f 34 20  |1,.eg 1 1/2 1/4 |
00000270  31 2f 38 20 31 2f 31 36  0a 53 3c 69 3e 3d 73 75  |1/8 1/16.S<i>=su|
00000280  6d 20 6f 66 20 74 65 72  6d 73 20 74 6f 20 69 6e  |m of terms to in|
00000290  66 69 6e 69 74 79 0a 61  3d 73 74 61 72 74 69 6e  |finity.a=startin|
000002a0  67 20 6e 75 6d 62 65 72  20 28 65 67 20 31 29 0a  |g number (eg 1).|
000002b0  72 3d 63 6f 6d 6d 6f 6e  20 72 61 74 69 6f 20 28  |r=common ratio (|
000002c0  65 67 20 bd 29 0a 65 3d  28 31 2f 30 21 29 2b 28  |eg .).e=(1/0!)+(|
000002d0  31 2f 31 21 29 2b 28 31  2f 32 21 29 2b 28 31 2f  |1/1!)+(1/2!)+(1/|
000002e0  33 21 29 2b 28 31 2f 34  21 29 2e 2e 2e 0a 54 68  |3!)+(1/4!)....Th|
000002f0  69 73 20 69 73 20 6f 6e  65 20 77 61 79 20 6f 66  |is is one way of|
00000300  20 63 61 6c 63 75 6c 61  74 69 6e 67 20 65 20 28  | calculating e (|
00000310  32 2e 37 31 38 29 2c 0a  77 68 65 72 65 20 61 21  |2.718),.where a!|
00000320  20 69 73 20 74 68 65 20  66 61 63 74 6f 72 69 61  | is the factoria|
00000330  6c 20 6f 66 20 61 3a 0a  61 28 61 2d 31 29 28 61  |l of a:.a(a-1)(a|
00000340  2d 32 29 28 61 2d 33 29  2e 2e 20 75 6e 74 69 6c  |-2)(a-3).. until|
00000350  20 61 2d 6e 3d 31 0a 4e  6f 74 65 3a 20 30 21 3d  | a-n=1.Note: 0!=|
00000360  31 0a 0a 0a 0a 0a 0a 0a  0a 0a 0a 0a 0a 0a 0a 0a  |1...............|
00000370  0a 0a 0a 0a 0a 0a 0a 0a  0a 0a 0a 0a 0a 0a 0a 0a  |................|
*
000003d0  0a 0a 0a 0a 0a                                    |.....|
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