Circle-ellipse problem

The circle-ellipse problem is about understanding what shapes are circles and which ones are ellipses. A circle is a shape with no corners that has all its sides the same length, like a wheel. An ellipse is also a shape with no corners, but it is longer in one direction than it is in the other direction, like an egg or an oval. To determine if a shape is a circle or an ellipse, you can measure the distance from one side of the shape to the opposite side. If they are the same length, then it is a circle. If they are different lengths, then it is an ellipse.