Answer:
Explanation:
If we half the base of the equilateral triangle, which has a length of xcm, we can form a right-angled triangle with a base of x/2 cm and height 2√3 cm.
Now using Pythagoras' Theorem we solve for the hypotenuse:

x must be positive as it is a length so we multiply 4 by 3 to get the perimeter of 12.