Perimeter of a triangle is 21 cm. The AB side is 2 times smaller than the CB side, and the CB side is 4 cm larger than the AC.

Perimeter of a triangle is 21 cm. The AB side is 2 times smaller than the CB side, and the CB side is 4 cm larger than the AC.  find the sides of the triangle ABC.

Let the length of AB be equal to x. Then the length of the CB is 2x, and the length of the AC is 2x-4.
Perimeter of triangle ABC:
P = AB + BC + CA = x + 2x + 2x-4 = 21.
5x + 4 = 21;
5x = 25;
x = 5.
AB = 5; BC = 10; AC = 6.
Answer: AB = 5; BC = 10; AC = 6.