Explain the geometric properties shown in the diagram.

Analysis of Geometric Properties:

• Circle and Center: The diagram shows a circle with center O. Points A, B, C, and D are on the circumference.
• Radii: Segments OC and OD are radii of the circle. This is indicated by the text 'OC = ___ радиусы' (OC = ___ radii) and the definition 'Окружность с центром О' (Circle with center O). All radii of a circle are equal in length. Therefore, OC = OD.
• Diameter: Segment AB passes through the center O and connects two points on the circumference. This means AB is a diameter of the circle.
• Chord: Segment CD is a chord of the circle.
• Perpendicularity: The diagram visually suggests that OM is perpendicular to CD, and AB is perpendicular to CD. The text 'высота ДCOD' (height of triangle COD) and the arrow pointing to OM imply that OM represents the height from O to CD. The arrangement of AB and CD suggests they are perpendicular.
• Midpoint: Point M appears to be the midpoint of CD, as indicated by the text 'M - середина CD' (M - midpoint of CD).
• Triangle COD: Triangle COD is an isosceles triangle because OC and OD are radii and thus equal in length.
• Triangle AOC: Triangle AOC is also an isosceles triangle because OA and OC are radii.
• Right Triangles: If OM is perpendicular to CD, then triangle OMD and triangle OMC are right-angled triangles. Similarly, if OM is the altitude and M is the midpoint of CD, and AB is perpendicular to CD, this implies symmetry.
• Relationship between AB and CD: Since AB is a diameter and appears perpendicular to chord CD at M, AB bisects CD. This is a property of circles: a diameter perpendicular to a chord bisects the chord.
• Segments: The text 'Отрезки ОС и OD' (Segments OC and OD) are explicitly mentioned as part of the additional construction.

Conclusion: The diagram illustrates fundamental properties of circles, including radii, diameters, chords, and the relationships between them, particularly when a diameter is perpendicular to a chord.