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MMO 007 Moscow MO 1935 system of arithmetic + geometric progression

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July 17, 2019
Arithmetic Progressionalgebrasystem of equationsgeometric progression

Problem Statement

Find four consecutive terms a,b,c,da, b, c, d of an arithmetic progression and four consecutive terms a1,b1,c1,d1a_1, b_1, c_1, d_1 of a geometric progression such that {a+a1=27 b+b1=27c+c1=39d+d1=87\begin{cases}a + a_1 = 27 \\\ b + b_1 = 27 \\ c + c_1 = 39 \\ d + d_1 = 87\end{cases}.