Х- второе число, 2х- первое; 2х+2,6 - третье число; по условию (х+2х+(2х+2,6))/3=13,2;
х+2х+2х+2,6=13,2*3;
5х=39,6-2,6;
5х=37;
х=37/5;
х=7,4
Обратная пропорциональность
<span>AB=BC=CD=DE=EF = x</span>
<span>AD:DF</span>
<span>AD = AB+BC+CD = 3x, DF=DE+EF = 2x => AD:DF = 3x:2x = 3:2</span>
<span>AC:AF</span>
<span>AC = AB+BC = 2x, AF=AB+BC+CD+DE+EF = 5x => AC:AF = 2:5</span>
<span>BD:CE</span>
<span>BD = BC+CD = 2x, CE = CD+DE = 2x => BD:CE = 1:1</span>
<span>BF:BD </span>
<span>BF = BC+CD+DE+EF = 4x, BD = BC+CD = 2x => BF:BD = 4:2 = 2:1</span>
Ответ:
3×11/18(61/6-311/21)=-8,511