Answer:
The length side of the triangle is 
Step-by-step explanation:
we know that
The equilateral triangle has three equal sides and three equal internal angles of measure of 60 degrees each.
Let
b------> the length side of the equilateral triangle
Applying Pythagoras theorem

Answer:
A
Step-by-step explanation:
The mean is all of them added together divided by the number, so multiple the mean by the number of sides, 3, and that's the perimeter. 18 x 3 = 54
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