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Across

3. A line segment, line, or plane that divides a geometric figure into two congruent halves.
4. A polyhedron whose one face is a polygon and the other faces are triangles with one common vertex. This polygon is the base of the pyramid. The other triangles are the lateral faces. The common vertex of these lateral faces is the vertex of the pyramid. The segment from the vertex perpendicular to the base is called the altitude of the pyramid. The length of the altitude is called the height of the pyramid. The intersections of the adjacent lateral faces are called the lateral edges of the pyramid.
8. A closed plane figure bounded by at least three line segments.
12. If the denominator of a is 0, then the fraction is undefined.
14. The distance around the outside of a plane figure. For a polygon, the perimeter is the sum of the lengths of the sides.
16. A point at which the two rays of an angle meet or the intersection point of two sides of a plane figure.
17. A 3D figure with a single base tapering to an apex. The base can be any simple closed curve. Often the word cone refers to a right circular cone.
19. The geometric figure formed by two points. A line is the straight path connecting two points and extending beyond the points in both directions.
20. A pair of numbers that describe the position of a point on a coordinate plane by using the horizontal and vertical distances from the two reference axes.
21. The side facing a given angle in a triangle. It is the side not forming one arm of the angle.
24. The pair of angles opposite each other formed by two intersecting lines.
28. A set of logical arguments used to deduce or prove a mathematical theorem from a set of axioms.
30. A planar surface of a solid figure.
31. Two acute angles that add up to 90° (40-50, 30-60, or 45-45)
34. An angle less than 90°
37. Also called half-line. It is a straight line that extends from a point.
38. A line segment where two faces of a polyhedron meet.
40. A perfect round ball. A sphere is a closed solid bounded by a surface on which all points are equidistant from a central point called the center.
41. An angle that measures 90° or /2 radians. It is the angle between two perpendicular lines such as the corner of a square or two perpendicular planes such as the wall and the ground.
42. If a middle point is on a line segment connecting two other points at the ends of the segment, that point is between the others.
44. polygon a shape/solid with a “cave”
46. It's easiest to just say that a convex is one that is NOT concave! A polygon is convex if you can draw straight lines that connect every single vertex and your lines never go outside the polygon. There is no cave!
47. Exactly equal in size and shape. Congruent sides or segments have the exact same length. Congruent angles have the exact same measure. For any set of congruent geometric figures, corresponding sides, angles, faces, etc. are congruent.
48. Also called non-coplanar lines. They are straight lines that are neither parallel, nor intersecting. They lie in different planes.

Down

1. A geometric object that has no dimension and is used to indicate a location.
2. An angle over 90 degrees and under 180 degrees.
4. A statement accepted as true without proof. A postulate should be so simple and direct that it seems to be unquestionably true.
5. A solid bounded by at least four polygonal faces. The pairs of faces meet along their edges. Three or more edges meet in each vertex. A diagonal of a polyhedron is a line segment joining two vertices that are not in the same face.
6. The point halfway between two given points.
7. An additional geometric figure that is constructed to assist in solving a problem or producing a proof.
9. At a 90° angle. Note: Perpendicular lines have slopes that are negative reciprocals.
10. A flat surface that can extend forever in length and width but has no thickness. The surface of a calm sea and a flat valley are all physical models of a plane.
11. A space figure with two parallel polygonal bases that are the same shape and the same size.
13. Two lines (lying in the same plane) are parallel if they never crosst... This means that the two lines are always the same distance apart.
15. The distance from the center of a circle to any point on its circumference.
18. Two angles in a plane which share a common vertex and a common side but do not overlap.
22. Two angles that add up to 180°.
23. A pair of adjacent angles formed by intersecting lines. Linear pairs of angles are supplementary.
25. A complete circular arc. Circumference also means the distance around the the outside of a circle.
26. Lying in the same plane. For example, any set of three points in space are coplanar.
27. The surface included within a closed figure, measured by the number of square units needed to cover the surface.
29. A unit of angle measure equal to of a complete revolution. There are 360 degrees in a circle. Degrees are indicated by the ° symbol, so 35° means 35 degrees.
32. All points between two given points
33. A line segment between two points on the circle or sphere which passes through the center. The word diameter is also also refers to the length of this line segment.
35. Lying on the same straight line.
36. A general conclusion proposed to be proved upon the basis of certain given hypotheses or assumptions; or, a general conclusion that has been proved, e.g., Pythagorean Theorem, Binomial Theorem, Fundamental Theorem of Algebra, etc.
39. A 3D geometric figure with parallel congruent bases. The bases can be shaped like any closed plane figure (not necessarily a circle) and must be oriented identically.
43. The side of a right triangle opposite the right angle. Note: The hypotenuse is the longest side of a right triangle.
45. Two rays sharing a common endpoint. measured in degrees or radians.