Ответ:    13 7/9 cm.

Пошаговое объяснение:

ABC is a triangle.

AB = 5 7/9 cm .

BC=? on 2 8/9 < AB =>

5 7/9 - 2 8/9 = 3 (7-8)/9 = 2 (9+7-8)/9 = 2 8/9cm

AC=? on 2 2/9 > BC=> 2 8/9+2 2/9 = 4 10/9 = 5 1/9 cm

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Perimeter P=AB+BC+AC;

P=5 7/9 + 2 8/9 + 5 1/9 = (5+2+5) (7+8+1)/9 = 12 16/9 = 13 7/9 cm