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If sum of all the solutions of the equation 1 2 1 6 cos 6 cos cos 8 = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − π ⋅ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + π ⋅ x x x in [0, π ] is k π , then k is equal to :

1. 3 2
2. 9 13
3. 9 8
4. 9 20

Correct answer: 9 13

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