Tolong dong bantuan nya Suku ke 5 suatu baris hitung =580 jumlah 7 suku pertama 3920 A. suku pertama ... B. beda antar suku C. suku ke 12 D. jumlah 12 suku pertama
Galladeaviero
U5 = 580 --> a+ 4b = 580 ...(1) . S7 = 3.920 --> s7 = 7/2 ( 2a +6b) = 3.920 7(a+3b) = 3.920 a+3b = 560...(2) .. (1) dan (2) a + 4b = 580 a+3b = 560 kurangkan, maka b = 20 a + 4b = 580 a = 580 - 4b --> a = 500 . U12 = a+ 11b= 500+ 11(20) = 770 . Sn = n/2 ( a + Un) S12 = 12/2 (500 + 770) = 7.620 ...
.
S7 = 3.920 -->
s7 = 7/2 ( 2a +6b) = 3.920
7(a+3b) = 3.920
a+3b = 560...(2)
..
(1) dan (2)
a + 4b = 580
a+3b = 560
kurangkan, maka b = 20
a + 4b = 580
a = 580 - 4b --> a = 500
.
U12 = a+ 11b= 500+ 11(20) = 770
.
Sn = n/2 ( a + Un)
S12 = 12/2 (500 + 770) = 7.620
...