Tentukan jumlah 20 Suku pertama dari barisan U3=8 U7=16
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Jawaban:
460
Penjelasan dengan langkah-langkah:
U3 = 8
a + 2b = 8 .... (1)
U7 = 16
a + 6b = 16 .... (2)
Eliminasi
a + 2b = 8
a + 6b = 16
________ –
-4b = -8
b = -8 ÷ (-4)
b = 2
Substitusi
a + 2b = 8
a + 2(2) = 8
a + 4 = 8
a = 8 - 4
a = 4
Suku ke-20
U20 = a + 19b
= 4 + 19(2)
= 4 + 38
= 42
Jumlah 20 suku pertama
S20 = 20/2 × (4 + 42)
S20 = 10 × 46
S20 = 460
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