Diketahui rumus suku ke-n suatu barisan aritmatika adalah U n=2n-7/4.jumlah 12 suku pertama dari barisan aritmatika tersebut adalah

diketahui rumus suku ke-n suatu barisan aritmatika adalah U n=2n-7/4.jumlah 12 suku pertama dari barisan aritmatika tersebut adalah

Barisan Aritmatika

Un = 2n – 7/4
U1 = a = suku pertama
U1 = 2.1 – 7/4 = 2 – 1 3/4 = 1/4

U12 = suku ke 12
U12 = 2.12 – 7/4 = 24 – 1 3/4 = 22 1/2

Sn = n/2 (a + Un)
Jumlah 12 suku pertama = S12

S12
= n/2 (a + U12)
= 12/2 (1/4 + 22 1/2)
= 6 × (22 + 3/4)
= 132 + 18/4
= 132 + 4 1/2
= 136 1/2
= 136,5

∴ Jumlah 12 suku pertama dari barisan aritmatika adalah 136,5.

Baca Juga :  Complete the sentences with a form of the verb in parentheses. Three hundred and fifty years ago, people (1. make) /made/ their own clothes. They (2. have, not) _____ machines for making clothes. There (3. be, not) _____ any clothing factories. People (4. tear) _____ homemade clothes that were sewn by hand. Today, very few people (5. make) _____ their own clothes. Clothing (6. come) _____ ready-made from factories. People (7. buy) _____ almost all their clothes from stores. The modern clothing industry (8. be) _____ international. As a result, people from different countries often (9. wear) _____ similar clothes. For example, people in many different countries throughout the world (10. wear) _____ jeans and t-shirts. However, some regional differences in clothing still (11. exist) _____ for instance, people of the Arabian deserts (12. wear) _____ loose, flowing lobes to protect themselves from the heat of the sun. In parts of Northern Europe, fur hats (13. be) _____ common in the winter. In the future, there (14. be, probably) _____ fewer and fewer differences in clothing. People throughout the world (15. wear) _____ clothes from the same factories. (16. We all, dress) _____ in the future? TV shows and movies about the future often (17. show) _____ everybody in a uniform of some kind. What (18. you, think) _____? Number 18

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