Diketahui deret 3 + 6 + 12 + 24 + 48 + … Tentukan U_{11} dan tolong jelaskan caranya…

Sn = n/2 + ( U1(2) + (n-1)b, S11= 11/2 + ( 6 + (10*3), s11= 5,5 + 36, S11 = 41,5, *sorry kalau salah*
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A=3, r=2, jawab, U11= U5. r^6, = 48. 2^6, = 48. 64, = 3072