MathDB
0<a,b,c,d<1 => 1 + ab + bc + cd + da + ac + bd > a+b+c+d

Source: JBMO 2008 Shortlist A6

October 14, 2017
JBMOalgebrainequalities

Problem Statement

If the real numbers a,b,c,da, b, c, d are such that 0<a,b,c,d<10 < a,b,c,d < 1, show that 1+ab+bc+cd+da+ac+bd>a+b+c+d1 + ab + bc + cd + da + ac + bd > a + b + c + d.
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