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Let _ k=1 ^ n a_ k = n²+ n . If a₁₀=59 and a₆=7 a₁ , then + is equal to

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Correct answer

D. 5

Step-by-step solution

S_n = n^2 + n a_n = S_n - S_ n-1 = (2n-1) + for n 1 . a₁₀ = 19 + = 59 ... (i) a₆ = 11 + , a₁ = + . a₆ = 7a₁ 11 + = 7 + 7 4 = 6 = 3 2 ... (ii) Substituting (ii) in (i): 19 3 2 + = 59 59 2 = 59 = 2 , = 3 . + = 5 .

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