Let x denote the length of the base AC of this isosceles triangle ABC.
In the initial data for this task, it is reported that the lateral side of AB is three times larger than the base of the AC, therefore, the length of the lateral side of AB should be a wound of 3 cm.
Since this triangle is isosceles, the length of its second lateral side BC should also be 3 cm wound.
According to the condition of the problem, the perimeter of this triangle is 140 cm, therefore, we can draw up the following equation:
x + 3x + 3x = 140,
solving which, we get:
7x = 140;
x = 140/7 = 20 cm.
We find the length of the side:
3x = 3 * 20 = 60 cm.
Answer: 20 cm, 60 cm and 60 cm.
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