Measure from any point of the shape to the other side. What do you notice about the widths?

With the usual small lip of a manhole, would this shape make a good cover?

Look around you and find some triangles. Decide which angle is the largest and check to see if it is opposite the longest side.

Cut a triangle from a piece of cardboard and see if it can easily fall through the hole formed where you cut it out.

On a card, draw a triangle with all sides the same length (an equilateral triangle).

Next, draw arcs around the triangle, using each corner as the center of a circle and the length of a side of the triangle as the radius. (See the diagram to right.)