Pola aritmatika diketahui U3+U7=0 dengan nilai U10=10 . Nilai U20 adalah A.20 B.25 C.30 D.35 E.40

u3 + u7 = 0
a + (3 - 1)b + a + (7 - 1)b =0
a + 2b + a + 6b = 0
2a + 8b = 0 ....(1)

u10 = a + (10 - 1)b
10 = a + 9b ....(2)

2a + 8b = 0 |1 |
a + 9b = 10 |2 |
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2a + 8b = 0
2a + 18b= 20
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-10b = -20
b = -20/-10
b = 2

2a + 8b = 0
2a + 8(2) = 0
2a + 16 = 0
2a = -16
a = -16/2
a = -8

u20 = -8 + (20 - 1)2
u20 = -8 + 38
u20 = 30

jawabannya c