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If cos –1 x – cos –1 2 y = α , where –1 ≤ x ≤ 1, – 2 ≤ y ≤ 2, x ≤ 2 y , then for all x, y, 4x 2 – 4xy cos α + y 2 is equal to :

1. 4 sin 2 α
2. 2 sin 2 α
3. 4 sin 2 α – 2x 2 y 2
4. 4 cos 2 α + 2x 2 y 2

Correct answer: 4 sin 2 α

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