An equilateral triangle is a triangle with sides that are all the same length. The perimeter is found by adding up the length of all sides of the triangle.
If one of the sides, the base, is 12cm, then that means the other two sides must also be 12cm. You have three sides, 12cm each. To find the perimeter, just add the lengths of the three sides:
[tex]perimeter = 12cm +12 cm+12 cm = 36 cm[/tex]
Your perimeter is 36 cm.
