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If a = ∞ → n lim ∑ = + n 1 k 2 2 k n n 2 and f(x) = x cos 1 x cos – 1 + , x ∈ (0, 1), then

1. 2 2 f ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a = f ′ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a
2. f ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a f ′ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a = 2
3. 2 f ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a = f ′ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a
4. f ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a = 2 f ′ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a

Correct answer: 2 f ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a = f ′ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ 2 a

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