, , , , q, . q - .
n-
n-
:
bn+1 =bn q, bn ≠ 0, q ≠ 0 | |
n- | bn = b1 q n-1 |
n | |
, q:
- , -
- , -
:
.
( ) :
1) ( ) .
2) ( ). n - :
,
3) a, b, c ( ) ,
(a 2 - bc)(b 2 - ac)(c 2 - ab) = 0, |
a, b, c ( ) ,
b 2 = ac.
4) S (| q | < 1)
:
n :
.
, k- , n- , :
:
, ,
.
():
ü , 1/2. 1/2, ,
ü 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192 2 .
ü 50; −25; 12,5; −6,25; 3,125; - .
1) b1, b2, b3,..., bn,....
, b1 = , q = - 3. b6
. n- .
n = 6 :
|
|
b6 = b1 q5 = (-3)5 = -162
-162.
2) 1728, 63. .
. b 1, b 2 b 3- . b 1 b 2 b 3 = 1728 b 2 = 12. ,
(. )
z 2 - 51 z + 144 = 0.
, = 3 = 48, , b 1 = 3, b 3 = 48 b 1 = 48, b 3 = 3. b 1 = 3, b 2 = 12 b 1 = 48 b 2 = 12, q = 4 q = 1/4. , = 3 q = 4 = 48 q = 1/4.
()
1) 1400 , 100 , . 5000 ?
: : 1400, 1300, , 1400-100(n-1). a1=1400; d=-100, Sn=5000.
! n. Sn= (2a1+ d (n-1))n:2;
5000= (2·1400-100 · (n-1)) n:2;
10000= (2800-100 n+100) n;
10000= (2900-100 n) n;
100 n2-2900 n+10000=0;
n2-29 n+100=0; n=25, n=4
n=4 ( n=25 n=-1000, n>0) , 4 .
: 4 .
()
2) , 7 8 . 7 , , 48 , 192 . 7 , ?