Hasil dari 3 1/2 : 2 3/4 + 5 1/2 .... dari suatu barisan aritmetika diketahui suatu suku ke -3 = 11 dan suku ke-9 = 23. jumlah 25 suku pertama adalah.....
auliaoktaviona
1. 7/2 x 4/11 + 11/2 = 14/11 14/11 + 11/2 = 6 17/22 2. U9 = a + 8b = 23...(1) U3 = a + 2b = 11...(2) (8b - 2b) = (23 - 11) 6b = 12 b = 2 (subtitusi ke (1) & (2))
U25 = a + 24b = 7 + 24 x 2 = 7 + 48 = 55 Sn = n/2 (a + Un) S25 = 25/2 (7 + 55) = 25/2 x 62 = 775 maaf kalo salah
14/11 + 11/2 = 6 17/22
2. U9 = a + 8b = 23...(1)
U3 = a + 2b = 11...(2)
(8b - 2b) = (23 - 11)
6b = 12
b = 2 (subtitusi ke (1) & (2))
U25 = a + 24b
= 7 + 24 x 2
= 7 + 48 = 55
Sn = n/2 (a + Un)
S25 = 25/2 (7 + 55)
= 25/2 x 62 = 775
maaf kalo salah