Jawaban dari tugas bilangan aritmetika di atas adalah sebagai berikut.

1. 161.
2. 276.
3. 1572.
4. 603.

Penjelasan dengan langkah-langkah:

Diketahui:

1. U4 = 3n -1
2. U1 = 12, U7 = 24
3. U3 = 18 U7 = 38
4. U3 = 14 U7 = 26

Ditanya:

1. U54?
2. S12?
3. S24?
4. S18?

Jawab:

No. 1

U54 = 3(54) -1 = 161

U1 = 12, U7 = 24

No. 2

a = 12

a + 6b = 24

6b = 12

b = 2

U12 = a + 11b = 12 + 11(2) = 12 + 22 = 34

Sn = x (a + Un)

S12 = 6 x (12 + 34) = 276

Soal. No.3

U3 = 18, U7 = 38

a + 2b = 18

a + 6b = 38

__________-

-4b = -20

b = 5 -----> a + 2(5) = 18 ----> a = 18 - 10 = 8

U24 = a + 23b = 8 + 23(5) = 123

S24 = 12 x (8 + 123) = 1572

Soal No.4

U3 = 14 U7 = 26

a + 2b = 14

a + 6b = 26

__________-

-4b = -12

b = 3

a + 2b = 14 ------> a + 2(3) = 14 ----> a = 14 - 6 = 8

U18 = a + 17b = 8 + 17(3) = 8 + 51 = 59

S18 = 9 x (8+59) = 603

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