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If sin^(4) alpha + 4 cos^(4) beta + 2 = ...

If `sin^(4) alpha + 4 cos^(4) beta + 2 = 4sqrt(2) sin alpha cos beta, alpha beta in [0, pi]`, then `cos (alpha + beta) - cos (alpha - beta)` is equal to `-sqrt(k)`. The value of k is _________.

A

`-sqrt(2)`

B

`0`

C

`sqrt(2)`

D

`-1`

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The correct Answer is:
A
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