geometry

1. flat surface that extends into infinity
3. an angle whose sides lie in opposite directions from the vertex in the same straight line and which equals two right angles
5. a part cut off from a figure, especially a circular or spherical one, by a line or plane
6. a measurement for angles
8. the exact middle point
11. an angle of 90°, as in a corner of a square or at the intersection of two perpendicular straight lines
12. a long, narrow mark or band
13. device used in geometry and technical drawing

1. an instrument for measuring angles, typically in the form of a flat semicircle marked with degrees along the curved edge
2. lines straight lines that do not intersect at any point
4. lines that are at right angles to each other
7. each angular point of a polygon, polyhedron, or other figure
9. an exact position or location on a plane surface
10. the space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet
11. part of a line that has a fixed starting point but no end point