Find the perimeter of an isosceles truncle if its side is 30 cm and the base is half of the side

1) Since the given triangle is isosceles, then its two sides are equal. The length of each of them is 30 cm.

2) Calculate the length of the base of this triangle, if it is known that it is half the length of its lateral side:

30: 2 = 15 cm.

3) The perimeter of a triangle is the sum of the lengths of all its sides. Let’s calculate what the perimeter of a given triangle is:

30 + 30 + 15 = 75 cm.

Answer: 75 cm.