This Problem Set is a part of the Lesson 2, Unit 3, Grade 7. In this lesson, students move from the informal idea of a circle as "a round figure" to the more formal definition that a circle is the set of points that are equally distant from the center, enclosing a circular region. Be introduced to the terms diameter, center, radius, and circumference. Learning targets: students can identify the diameter, center, radius, and circumference of a circle.