geometry

6. x or y
8. at an angle of 90° to a given line, plane, or surface.
10. a parallelogram with opposite equal acute angles, opposite equal obtuse angles, and four equal sides.
13. a half of a circle or of its circumference.
14. at equal distances.
15. the conceptual operation of inverting a system or event with respect to a plane, each element being transferred perpendicularly through the plane to a point the same distance the other side of it.
17. a general proposition not self-evident but proved by a chain of reasoning; a truth established by means of accepted truths.
18. a solid or hollow object which tapers from a circular or roughly circular base to a point.
19. a plane figure with five straight sides and five angles.
21. relating to geometry, or according to its methods.
24. a unit of angle, equal to an angle at the center of a circle whose arc is equal in length to the radius.
25. the gradient of a graph at any point.

1. (of a quantity) having only magnitude, not direction.
2. a plane figure with eight straight sides and eight angles.
3. never intersect
4. a half of a sphere.
5. not collinear
7. a way, especially one of several possible variations, in which a set or number of things can be ordered or arranged
9. cot coplanar
11. longest side of a triangle
12. A tangent is an object, like a line, which touches a curve.
13. (of a pair of lines) neither parallel nor intersecting.
16. a quadrilateral with only one pair of parallel sides.
20. the point or place where something begins, arises, or is derived.
22. Side a straight line that has been rotated around a point on another line to form an angle measured in a clockwise or counterclockwise direction
23. evenly divisible only by itself and one