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The value of ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π 7 6 cos 7 4 cos 7 2 cos is equal to :

1. –1
2. 2 1 −
3. 3 1 −
4. 4 1 −

Correct answer: 2 1 −

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