carilah suku ke 21 dalam barisan aritmatika dimna suku ke 5=41dan suku ke 11=23
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Barisan aritmatika
Un = a + (n - 1)b
• Suku ke-5
U5 = a + (5 - 1)b
U5 = a + 4b
a + 4b = 41 ... (Pers. 1)
• Suku ke-11
U11 = a + (11 - 1)b
U11 = a + 10b
a + 10b = 23 ... (Pers. 2)
• Eliminasi pers. 2 dan 1
a + 10b = 23
a + 4b = 41
_________-
6b = -18
b = -18/6
b = -3
• Cari nilai a
a + 10b = 23
a + 10(-3) = 23
a - 30 = 23
a = 23 + 30
a = 53
• Suku ke-21
U21 = 53 + (21 - 1)(-3)
U21 = 53 + (20)(-3)
U21 = 53 - 60
U21 = -7
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