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Let ƒ : N → R be a function such that ƒ(x + y) = 2ƒ(x) ƒ(y) for natural numbers x and y. If ƒ

1. = 2, then the value of α for which ∑ = + α 10 1 k ) k ƒ( = ) 1 2 ( 3 512 20 − holds, is :
2. 2
3. 3
4. 4 (4) 6

Correct answer: 3

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