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Omni-MATH / Let a₁,a₂,⋯,a₄₁∈R, such that a₄₁=a₁,∑_(i=1)⁴⁰a_(i)=0, and for any i=1,2,⋯,40,|a_(i)−a_(i+1)|≤1. Determine the greatest possible value of (1)a₁₀+a₂₀+a₃₀+a₄₀; (2)a₁₀⋅a₂₀+a₃₀⋅a₄₀.

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problem

Let a1,a2,,a41R,a_1,a_2,\cdots,a_{41}\in\mathbb{R}, such that a41=a1,i=140ai=0,a_{41}=a_1, \sum_{i=1}^{40}a_i=0, and for any i=1,2,,40,|aiai+1|1.i=1,2,\cdots,40, |a_i-a_{i+1}|\leq 1. Determine the greatest possible value of (1)a10+a20+a30+a40;(1)a_{10}+a_{20}+a_{30}+a_{40}; (2)a10a20+a30a40.(2)a_{10}\cdot a_{20}+a_{30}\cdot a_{40}.
Plain-text mathematical notation (without MathML)
Let a₁,a₂,⋯,a₄₁∈R, such that a₄₁=a₁,∑_(i=1)⁴⁰a_(i)=0, and for any i=1,2,⋯,40,|a_(i)−a_(i+1)|≤1. Determine the greatest possible value of
(1)a₁₀+a₂₀+a₃₀+a₄₀;
(2)a₁₀⋅a₂₀+a₃₀⋅a₄₀.
Original LaTeX notation
Let $a_1,a_2,\cdots,a_{41}\in\mathbb{R},$ such that $a_{41}=a_1, \sum_{i=1}^{40}a_i=0,$ and for any $i=1,2,\cdots,40, |a_i-a_{i+1}|\leq 1.$ Determine the greatest possible value of
$(1)a_{10}+a_{20}+a_{30}+a_{40};$
$(2)a_{10}\cdot a_{20}+a_{30}\cdot a_{40}.$

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