Matematika 8. Dari barisan aritmatika diketahui U2+ U4= 20, U9-U5 = 12. Nilai U3+U6=... a.25 b.26 c.28 d.29pakai cara​

bethanykshlerinulv – April 07, 2023

8. Dari barisan aritmatika diketahui U2+ U4= 20, U9-U5 = 12. Nilai U3+U6=...
a.25
b.26
c.28
d.29
pakai cara​

Jawab:

Penjelasan dengan langkah-langkah:

U2 + U4= 20,

U9 - U5 = 12,

U3 + U6 = ...?

Un = a + (n - 1)b

U2 = a + (2 - 1)b = a + b

U4 = a + (4 - 1)b = a + 3b

U5 = a + (5 - 1)b = a + 4b

U9 = a + (9 - 1)b = a + 8b

a + b + a + 3b = 20

2a + 4b = 20

a + 8b - a - 4b = 12

4b = 12

b = 12/4 = 3

2a + 4(3) = 20

2a + 12 = 20

2a = 20 - 12

2a = 8

a = 8/2 = 4

U3 + U6 = a + (3 - 1)b + a + (6 - 1)b

U3 + U6 = a + 2b + a + 5b

U3 + U6 = 2a + 7b

U3 + U6 = 2(4) + 7(3)

U3 + U6 = 8 + 21

U3 + U6 = 29

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