" Life is not a problem to be solved but a reality to be experienced! "
© Copyright 2013 - 2024 KUDO.TIPS - All rights reserved.
a)an
12,15,18,21,
a1=12
r = a2-a1
r=15-12
r=3
an = a1 + (n-1)r
a100 = 12 + (100-1)3
a100 = 12 + 99*3
a100 = 12 + 297
a100 = 309
Sn = (a1+an)/2 * n
S100 = (a1+a100)/2 *100
S100 = 12+309 / 2 * 100
S100 = 160,5 * 100
S100 = 16050
b) tworzę podciąg bn ( zawierający parzyste wyrazy ciągu an)
b1 = a2 = 15
b2 = a4 = 21
b3 = a6 = 27
r = b2-b1
r = 21-15
r = 6
b40 = 15+(40-1)*6
b40 = 15 + 39*6
b40 = 15 + 234
b40 = 249
S40 = (15+249) / 2 * 40
S40 = 264/2 *40
S40 = 132 * 40
S40 = 5280
c) tworzę podciąg cn ( zawierający wyrazy ciągu an o numerach podzielnych przez 3 )
c1 = a3 = 18
c2 = a6 = 27
c3 = a9 = 36
r = c2-c1
r = 27-18
r=9
c40 = 18 + (40-1)*9
c40 = 18 + 39*9
c40 = 18 + 351
c40 = 369
S40 = (18 + 369) / 2 * 40
S40 = 387/2 * 40
S40 = 193,5*40
S40 = 7740