Cut out the shape and see whether it would fall through the hole left in the card. 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.)
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