A board with a slot circular with equally spaced pegs arranged on the circumferences of the circle and one peg at the Centre. Circle theorem can be used for the following:

• 1. • Semicircle Theorem: On the geoboard, stretch a rubber band across the diameter (e.g., pegs forming a semicircle base) and form a triangle with a point on the circumference. Measure the angle at the circumference (should be 90°). Alternatively, use the Angles in a Semicircle board to place a 90° angle piece at the circumference subtended by the diameter.
     • Angle at Center vs. Circumference: On the Angle at the Centre board, place an angle cutout (e.g., 30°) at the circumference subtended by an arc, then place two such cutouts at the center to show the center angle is 60° (twice 30°). On the geoboard, form an arc with rubber bands and measure the center angle (e.g., 60°) and circumference angle (30°).
     • Angles in Same Segment: On the geoboard, form a chord and two angles in the same segment (e.g., angles at two points on the circumference subtended by the chord). Measure to confirm they are equal.