# Circle FAQs:

Q: Is a circle a simple closed shape in Euclidean geometry?

A: Yes.

Q: Is a circle an ellipse with an eccentricity of zero?

A: Yes, and meaning that the two foci coincide with each other as the centre of the circle.

Q: Is a circle a highly symmetric shape: every line through the centre forms a line of reflection symmetry and it has rotational symmetry around the centre for every angle?

A: Yes.

Q: Is a circle sometimes said to be drawn about two points?

A: Yes.

Q: Is a circle the basis for the wheel?

A: Yes, and which, with related inventions such as gears, makes much of modern machinery possible.

Q: Is a circle also a different special case of a Cartesian oval in which one of the weights is zero?

A: Yes.

Q: Is a circle the shape with the largest area for a given length of perimeter?

A: Yes.

Q: Are circles actually circles: a generalised circle is either a circle or a line?

A: Yes.

Q: Is a circle subtended by the same chord and on the same side of the chord?

A: Yes, and then the central angle is twice the inscribed angle.

Q: Is a circle the plane curve enclosing the maximum area for a given arc length?

A: Yes.

Q: Is a circle only the boundary and the whole figure is called a disc?

A: Yes.

Q: Is a circle the problem?

A: Yes, and proposed by ancient geometers, of constructing a square with the same area as a given circle by using only a finite number of steps with compass and straightedge.

Q: Is a circle a tangent to the circle?

A: Yes.

Q: Is a circle a plane figure bounded by one line?

A: Yes, and such that all right lines drawn from a certain point within it to the bounding line, are equal.

Q: Is a circle a simple closed curve which divides the plane into two regions: an interior and an exterior?

A: Yes.

Q: Is a circle the simplest example of this type of figure?

A: Yes.

Q: Are circles similar?

A: Yes.