How many sides does a circle have? My son is in 2nd grade.  His math teacher gave the class a quiz, and one question was this:


  If a triangle has 3 sides, and a rectangle has 4 sides, 
  how many sides does a circle have?


My first reaction was "0" or "undefined".  But my son wrote "$\infty$" which I think is a reasonable answer.  However, it was marked wrong with the comment, "the answer is 1".

Is there an accepted correct answer in geometry?

edit: I ran into this teacher recently and mentioned this quiz problem.  She said she thought my son had written "8." She didn't know that a sideways "8" means infinity.
The answer depends on the definition of the word "side." I think this is a terrible question (edit: to put on a quiz) and is the kind of thing that will make children hate math. "Side" is a term that should really be reserved for polygons.
One way to understand the question and demonstrate applicability is to consider the problem and efficiency of finding the area of the union of 2 overlapping circles versus 2 overlapping rectangles or squares.

Let us now constrain the union area to be constant. 

In the case of circles it will always be the same shape, no matter which way the circles are positioned in relation to one another.

In the case of squares, it would be the same shape too.

In case of rectangles, the shape would vary.

We could here argue that the circle and square both have 1 side, because they are defined by a single length (radius or diagonal), or in other words, they have no apparent "orientation".