Tentukanlah jumlah bilangan kelipatan 4 di antara bilangan 10 hingga 100.
Jawaban
awal = 12
beda = 4
Un = 96
Un = a + (n – 1)b
96 = 12 + (n – 1)4
96 = 12 + 4n – 4
96 = 8 + 4n
4n = 96 – 8
4n = 88
n = 88/4
n = 22
Sn = n/2 (a + Un)
= 22/2 (12 + 96)
= 11 (108)
= 1188
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