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The value of ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + ∑ ∑ = = − 19 1 n n 1 p 1 p 2 1 cot cot is -

1. 23 22
2. 22 23
3. 19 21
4. 21 19

Correct answer: 19 21

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