To do this, all you need is to draw triangle with each side being 7 cm, and a circle that intersects all three of its corners.
Step-by-step explanation:
With a ruler and a pencil, draw a 7cm line.
With a compass set to a radius of 7cm draw an arc centered around the right end of the line.
With the same compass, still at 7cm, draw an arc centered around the left end of the line.
These two arcs will intersect on either side of the line (you only need one side, so you only need a small arc in the right place, roughly where you think the third point if the triangle is.
Where those arcs intersect is the third point on your triangle. Mark that, and then trace two lines from that point to either end of the line segment you started with.
<em>You now have an equilateral triangle with 7cm sides. Next you need to draw the circle</em>
Measure the halfway point on two of your three lines.
Draw a line from that each of those halfway points to the opposite corner. The new lines you're drawing will be perpendicular to the edge your measuring against.
You have now drawn two line segments, and they intersect in the center of the circle. Now take your compass and set its radius to the distance from that center point to one of the three corner points.
Centered on that middle point, trace a circle with the selected radius.
