Answer:
Diagram 1
Draw a circle with a radius of 8 cm, ensuring you have clearly marked the center point (black circle with center C1)
Add a point on the circumference of the circle (point C2)
Draw a second circle of radius 8cm with point C2 as its center (red circle with center C2).
Diagram 2
The red circle intersects the black circle at two points (D and E).
Connect these 2 points of intersection with a line segment.
Diagram 3
Draw a third circle with center D and radius DE (shown in blue)
This circle intersects the black circle at point F.
Diagram 4
Draw 2 line segments to connect points D and E with point F - this is your equilateral triangle inside the circle!