jika diketahui barisan aritmatika 24 21 18 15 .....tentukan jumlah 20 suku pertamanya
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Penjelasan dengan langkah-langkah:
24,21,18,15
a = 24
b = 21 - 24
b = -3
n = 20
Un = a + (n - 1)b
U20 = 24 + (20 - 1)-3
U20 = 24 + (19)-3
U20 = 24 + (-57)
U20 = -33
Sn = n/2 (2a + (n - 1)b)
S20 = 20/2 (2(24) + (20 - 1)-3)
S20 = 10 (48 + (19)-3)
S20 = 10 (48 + (-57)
S20 = 10 (-9)
S20 = -90
Jawaban:
24, 21, 18,15,,,
a = 24
b = 21-24 = -3
U20 = a + b19
= 24 + (-3)(19)
= 24 - 57
= - 33
S20 = n/2 × ( a + Un)
S20 = 20/2 × ( 24 + (-33))
S20 = 10 × -9
S20 = -90
jadi jumlah 20 suku pertama = -90
[answer.2.content]
