Circle and disc
Tell a circle from a disc, find the centre and radii and mark the points that lie on the circle.
📖 Start here: read the steps of the “Lesson” in order (1, 2, 3 …) and answer each question. Then continue with “Practice”.
- Palestine: grade 2
- Ukraine: grade 2
- Russia: grade 4
Guide
In the Grade 2 book (NUSH) a circle is a line, and a disc is the part of the plane that the line bounds. The boundary of a disc is a circle. A circle is drawn with a compass.
The centre is the point in the middle of the circle, the same distance from all the points of the circle. A radius is a segment joining the centre to a point of the circle. A circle has infinitely many radii, all equal. A segment joining two points of the circle but not through the centre is not a radius.
A point can lie on the circle, inside the disc or outside it. To find out whether a point lies on the circle, check whether its distance to the centre is the radius.