Diketahui suku ke-5 dan suku ke-8 barisan aritmatika masing-masing 16 dan 25.Jumlah 22 suku pertama adalah....

2
U5 = 16
U8 = 25
pakai eliminasi
U5 = a + 4b = 16
U8 = a + 7b = 25
-3b = -9
b = -9/-3 = 3

a + 4b = 16
a + 4(3) = 16
a + 12 = 16
a = 16-12 = 4

Rumus
Sn=n : 2 (2a + (n-1)b )
S22 = 22 : 2 (2 (4) + (22-1) (3) )
= 11 ( 8 + (21)(3) )
= 11 (8 +63 )
= 11 . 71
= 781

Jawabanmu

2014-05-03T15:12:43+07:00
Beri yang Terbaik :)
U5 = 16
U8 = 25
rumus Un = a + (n-1) b
U5 = a + 4b = 16
U8 = a + 7b = 25
pakai eliminasi = -3b = -9
b = 3.
U5 = a + 4b = 16
a + 4.3 = 16
a = 16 - 12
a = 4.
U22 = a + 21b
4 + 21.3
4 + 63.
U22 = 67 .


di soal jawabannya :
A. 451
B. 781
C. 814
D. 902
BERI YG TERBAIK :)
Jawaban paling cerdas!
2014-05-03T15:30:43+07:00
U5 = 16
U8 = 25
pakai eliminasi
U5 = a + 4b = 16
U8 = a + 7b = 25
-3b = -9
b = -9/-3 = 3

a + 4b = 16
a + 4(3) = 16
a + 12 = 16
a = 16-12 = 4

Rumus
Sn=n : 2 (2a + (n-1)b )
S22 = 22 : 2 (2 (4) + (22-1) (3) )
= 11 ( 8 + (21)(3) )
= 11 (8 +63 )
= 11 . 71
= 781

jadikan yg terbaik ya :D
2 5 2