Basic geometry

5. a quadrilateral the opposite sides of which are parallel
7. a quadrilateral the sides of which are of equal length
8. a straight line which has exactly one point in common with a circle
9. the set of points of the plane which are at a given distance from a given point
13. an eight-sided polygon
15. two straight lines are ... if they have a common point
16. a quadrilateral two and two adjacent sides of which are of equal length
17. a ten-sided polygon
18. if all the sides of a triangle are of equal length, then it is an ... triangle
19. if two sides of a triangle are of equal length, then it is an ... triangle

1. a straight line passing through the midpoint of a line segment which is perpendicular to it
2. the set of points of the space which are at a given distance from a given point
3. a six-sided polygon
4. if a planar figure is not convex, then it is ...
6. an angle between 0 and 90 degrees
10. a quadrilateral all angles of which are right angle
11. the sum of the ... angles of a triangle is 180 degrees
12. a chord of the circle which is twice as long as the radius
14. a quadrilateral all sides and all angles of which are equal