Dik: suku ke-5 = 70 dan jumlah suku ke-7 = 462
Dit: 1. suku pertama.?
2. beda.?
Dit: 1. suku pertama.?
2. beda.?
tantikris43
U5 = 70. a + 4 b = 70 a = 70-4b S7 = 7/2 ( a + u7) = 7/2 (a + a + 6b) 462 = 7/2 ( 2a + 6b) 924 = 14a + 42b Subtitusikan a = 70- 4b ke 924 = 14a + 42b 924 = 14(70 -4b) + 42b 924 = 980 - 56b + 42b 924 = 980 - 14b 14b = 980 - 924 14b = 56 b = 56:14 = 4 a = 70- 4b = 70 - 16 = 54 Jadi suku pertama = a = 54 dan beda = b = 4
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