In an isosceles triangle ABC, the side AB is 7 cm and the perimeter is 17 cm Calculate the base of BC.

Let us denote the length of the base of this isosceles triangle through s.

Since in any isosceles triangle the sides are equal, then, according to the condition of the problem, the lengths of the sides of this triangle are 7 cm each.

Also in the condition of the problem it is said that the sum of the lengths of all three sides of this triangle is 17 cm, therefore, we can draw up the following equation:

7 + 7 + c = 17,

solving which, we get:

14 + c = 17;

14 + s – 14 = 17 – 14;

c = 3 cm.

Answer: the length of the base is 3 cm.