What is the radius of a circle with the equation ?

If the center of a circle is at (0,4) and the diameter of the circle is 6, what is the equation of that circle?

The above figure shows a circle on the coordinate axes with its center at the origin. The shaded region has area .

Give the equation of the circle.

The above figure shows a circle on the coordinate axes with its center at the origin. has length .

Give the equation of the circle.

What is the equation for a circle of radius 12, centered at the intersection of the two lines:

and

?

Circle A is given by the equation . Circle A is shifted up five units and left by six units. Then, its radius is doubled. What is the new equation for circle A?

The following circle is moved spaces to the left. Where is its new center located?

A square on the coordinate plane has vertices at the points with coordinates , , , and . Give the equation of the circle that circumscribes the square.

A circle with a radius of five is centered at the origin. A point on the circumference of the circle has an x-coordinate of two and a positive y-coordinate. What is the value of the y-coordinate?

A circle has its origin at . The point is on the edge of the circle. What is the radius of the circle?