Circles and measurement: a. Know that a circle is a two-dimensional shape created by connecting all of the points equidistant from a fixed point called the center of the circle. b. Understand and describe the relationships among the radius, diameter, and circumference of a circle. c. Understand and describe the relationship among the radius, diameter, and area of a circle. d. Know the formulas for the area and circumference of a circle and solve problems. e. Give an informal derivation of the relationship between the circumference and area of a circle.