What is the area of an equilateral triangle with a circumference of 12 cm?

What is the area of an equilateral triangle with a circumference of 12 cm?

Do a high, Pythagorean theorem
The hypotenuse, which is the waist of an equilateral triangle, is 4cm long
A right angle side, which is half of the bottom of an equilateral triangle, is 2 cm long
The other right side, the height of the regular triangle, is twice the length of the root 3
The area is 1 / 2 * 4 * 2 times root number 3 = 4 root number 3
(understand the following, I won't root)

An equilateral triangle has a circumference of 15 cm and a height of about 4 cm. What is the area of this triangle?

For equilateral triangle, if the perimeter is 15cm, the side length is 15 / 3 = 5cm
Area = 1 / 2 * bottom * height = 1 / 2 * 5 * 4 = 10 square centimeter