Jawaban:
-15
Penjelasan dengan langkah-langkah:
U2 + U5 = a + b + a + 4b = 5
2a + 5b = 5
U7 - U3 = a + 6b - (a + 2b) = 20
4b = 20
— persamaan
b = 5
— substitusi
2a + 5(5) = 5
2a + 25 = 5
2a = -20
a = -10
— jumlah 3 suku pertama
S3 = 3/2(2(-10) + 5(3-1))
= 3/2 x (-20 + 10)
= 3/2 x -10
= 3 x -5
= -15
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Jawaban:
-15
Penjelasan dengan langkah-langkah:
U2 + U5 = a + b + a + 4b = 5
2a + 5b = 5
U7 - U3 = a + 6b - (a + 2b) = 20
4b = 20
— persamaan
2a + 5b = 5
b = 5
— substitusi
2a + 5(5) = 5
2a + 25 = 5
2a = -20
a = -10
— jumlah 3 suku pertama
S3 = 3/2(2(-10) + 5(3-1))
= 3/2 x (-20 + 10)
= 3/2 x -10
= 3 x -5
= -15