A triangle has its vertices at the points with coordinates , , and . Give the equation of the circle that circumscribes it.

Refer to the above diagram. The circle has its center at the origin; is the point . What is the length of the arc , to the nearest tenth?

Refer to the above figure. The circle has its center at the origin. What is the equation of the circle?

On the coordinate plane, the vertices of a square are at the points with coordinates . Give the equation of the circle.

Find the diameter of the circle with the equation .