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|ax+b|+|cx+d|=|ex+f| - All-Russian MO 2001 Regional (R4) 8.5

Source:

September 25, 2024
algebra

Problem Statement

Let a,b,c,d,ea, b, c, d, e and ff be some numbers, and ace0 a \cdot c \cdot e \ne 0.It is known that the values of the expressions ax+b+cx+d|ax+b|+|cx+d| and ex+f|ex+f| equal at all values of xx. Prove that ad=bcad = bc.