Unit 9 (Copyrighted Vocab.) By-Osmund

Polygons are 2-dimensional shapes. They are made of straight lines, and the shape is "closed" (all the lines connect up).
the space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.
acute angle(acute)
an angle that is less than 90°.
Obtuse angle
an angle that is greater than 90° but
less than 180°
right angle
an angle that is 90° exactly
straight angle
an angle that is 180° exactly
Sides that are the same size and legnth are congruent
hatch mark
Marks that show congruence
Line Segment
The part of a line that connects two points.

It has definite end points.

Adding the word "segment" is important, because a line normally extends in both directions without end.

Try moving points "A" and "B":
A line with a start point but no end point (it goes to infinity)

Try moving points "A" and "B":
A point where two or more straight lines meet. A corner.

• any corner of this pentagon (a plane shape)
• any corner of this tetrahedron (a solid)

The plural of vertex is "vertices".
The dividing line is called the "bisector"
The point were two lines meet across
A straight line inside a shape that goes from one corner to another (but not an edge).

So when we join any two corners (called "vertices") which are not already joined by an edge, we get a diagonal.
Parallel Lines
Lines are parallel if they are always the same distance apart (called "equidistant"), and will never meet. Just remember:
Perpendicular Lines
Lines that intersect to form a 90 degree angle
is a line that divides a line segment into two equal parts. It also makes a right angle with the line segment. Each point on theis the same distance from each of the endpoints of the original line segment.
Plane Figure (two-dimensional)
A shape that only has two dimensions (such as width and height) and no thickness. Squares, Circles, Triangles, etc are two dimensional objects. Also known as "2D". See: Three-Dimensional. Plane Geometry.
A trapezoid is a 4-sided flat shape with straight sides that has a pair of opposite sides parallel.
Isosceles Trapezoid
In Euclidean geometry, an isosceles trapezoid (isosceles trapezium in British English) is a convex quadrilateral with a line of symmetry bisecting one pair of opposite sides. It is a special case of a trapezoid.
Right Trapezoid
A right trapezoid is a trapezoid that has at least two right angles. Below is a picture of a right trapezoid.
a four-sided plane rectilinear figure with opposite sides parallel.
Polygons are 2-dimensional shapes. They are made of straight lines, and the shape is "closed" (all the lines connect up).
A 4-sided flat shape with straight sides where all sides have equal length.

Also opposite sides are parallel and opposite angles are equal.

It is a type of parallelogram.
A 4-sided flat shape with straight sides where:

• all sides have equal length, and
• every interior angle is a right angle (90°)

It is a Quadrilateral and a Regular Polygon
A 4-sided flat shape with straight sides that:

• has two pairs of sides.
• each pair is made of two adjacent sides (they meet) that are equal in length.

Also, the angles are equal where the pairs meet.

The dashed lines are diagonals, which meet at a right angle. And one of the diagonals bisects (cuts equally in half) the other.