Answer: Connect the two circles together using the compass.
Steps to inscribe an equilateral triangle into a circle:
1. You are given a circle with the center marked.
2. Draw a radius of the circle using your straightedge.
3. Keep your compass open to the width of the radius and place it on the point where the radius and circle intersect.
4. Swing an arc the length of the radius that intersects the circle to the left of the radius originally drawn.
5. Keeping your compass at the same width, place it on the new intersection point you created in the previous step.
6. Continue this process until six points of intersection exist on the circle.
7. Connect together the first, third, and fifth intersection points.