Jawabanmu

2014-03-26T19:47:19+07:00
A. 
S₁₀ = 5(2a + 9b)
55 = 10a + 45b

U₁ = a = 1, subtitusikan nilainya

55 = 10 + 45b
45b = 45
b = 1

U₁₂ = a + 11b
      = 1 + 11
      = 12


B.
10 + 21 + 32 + 43 + 54

b = U₂ - U₁
   = 21 - 10
   = 11


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