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Algebra Difficulty 8.1 Shortlist Find the answer

Determine whether or not there exist 15 integers m1,,m15m_1,\ldots,m_{15}
such that~
k=115mkarctan(k)=arctan(16).\eqno(1)\displaystyle \sum_{k=1}^{15}\,m_k\cdot\arctan(k) = \arctan(16). \eqno(1)

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A number or a short expression. Spacing and $ signs are ignored.

Solution

We need to determine whether there exist 15 integers m1,m2,,m15 m_1, m_2, \ldots, m_{15} such that k=115mkarctan(k)=arctan(16). \sum_{k=1}^{15} m_k \cdot \arctan(k) = \arctan(16).

The strategy involves properties of the tangent and arctangent functions. The goal is to express arctan(16)\arctan(16) as a combination of arctan(k)\arctan(k) terms.

### Using the Addition Formula for Arctan:
Recall the formula for the addition of arctangents:
arctan(a)+arctan(b)=arctan(a+b1ab), \arctan(a) + \arctan(b) = \arctan\left(\frac{a + b}{1 - ab}\right),
provided that ab<1ab < 1.

### Initial Observations:

1. For arctan(k)\arctan(k) where 1k15 1 \leq k \leq 15 , the product k×16k \times 16 exceeds 1. Hence direct application of the addition formula with 16 as a combination with these integers is not straightforward.

2. Expressing arctan(16)\arctan(16) using integers 1 to 15 implies constructing a sequence of arctangent additions resulting in the composite form, which would balance the arctangent on the left.

### Exploring Possible Combinations:

An attempt to find a consistent set of integers mk m_k such that:

k=115mkarctan(k)=arctan(16) \sum_{k=1}^{15} m_k \cdot \arctan(k) = \arctan(16)

fails when it comes to precisely reconstructing arctan(16) \arctan(16) due to the restriction k=115mkk>16 \sum_{k=1}^{15} m_k \cdot k > 16 , meaning that the computations (a+b)/(1ab)(a+b)/(1-ab) do not align to produce arctan(16)\arctan(16) as all products ab1 ab \geq 1 .

### Conclusion:

Since no combination of integers m1,m2,,m15 m_1, m_2, \ldots, m_{15} satisfies the original equation by using integer multiples of arctan(k)\arctan(k) to yield arctan(16)\arctan(16), there can be no such combination existing.

Therefore:
No \boxed{\text{No}}

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