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Kelas : IX SMP
Bab : Barisan dan deret
Pembahasan :
Un = 99
2n - 1 = 99
2n = 100
n = 50
1 + 3 + 5 + ... + 99 = n²
1 + 3 + 5 + ... + 99 = 50²
1 + 3 + 5 + ... + 99 = 2500
99 = 1 + (n-1)2
99 = 1 + 2n - 2
99 = 2n - 1
99 + 1 = 2n
100 = 2n
n = 50
S50 = n/2 (2.a + (n-1)b)
= 50/2(2.1 + (50-1)2)
= 50/2(2 + 98)
= 25(100)
= 2500