Grade 8 Math

Vocabulary Terms

transformation

A rule that assigns each point in a plane to another point

pre-image

The original geometric object before the transformation

rigid motion

transformation that results in image that is congruent to pre-image

Reflect

a mirror image when we reflect a geometric image across a line

Line of Reflection

perpendicular bisector

Point

physical location in space that has no length, width or depth and is usually represented by a dot.

Congruent

geometric objects that are identical in shape and size

Vertical lines

lines parallel to the y -axis

Horizontal lines

lines parallel to the x-axis

Line

a set of connected points that extends forever in both directions

Collinear

When three points all lie on the same line

Ray

a portion of a line that has a starting point and then extends forever in one direction

Segment

a portion of a line that has both a starting and an ending point

Angle

defined as two rays that share the same starting point

Acute angle

an angle that measures less than 90 degrees.

obtuse angle

an angle that measures between 90 and 180 degrees

Right angle

an angle that measures exactly 90 degrees.

Straight angle

an angle that measures exactly 180 degrees.

Adjacent angles

two nonoverlapping angles that share a ray

Vertical angle pairs

pairs of angles that share a vertex point and have rays that point in opposite directions. Their measures are equal.

Complementary angles

two angles whose measures add up to 90 degrees.

Supplementary angles

two angles whose measures add up to 180 degrees.

Terminology

fancy work for specific vocabulary that applies to certain knowledge or study

Midpoint

one unique point that lies at the center of a line segment

Bisector

cuts a geometric object into two of the same types of objects that have the same measure. (segment bisector, angle bisector)

Perpendicular

two line segments or rays that form right angles with each other

Parallel

two lies in a plane that share no points in common, never intersect and two rays or line segments that lie on two parallel lines

Trapezoid

four-sided figure with at least one pair of parallel sides

Parallelogram

four sided figure with exactly two pair of parallel sides

Transversal

when two parallel lines are crossed by a third line (creates 8 angles)

corresponding angles

angles located in the same relative position on the two parallel lines and have equal measure

Interior angles

when eight angles are formed by two parallel lines cut by a transversal, four of them lie “inside” the parallel lines

same side interior angles

when eight angles are formed by two parallel lines cut by a transversal, the angles on the same side of the transversal (inside parallel lines) and add up to 180 degrees

Exterior angles

when the eight angles are formed by two parallel lines cut by a transversal, four of them like outside the parallel line

same side exterior angles

when eight angles are formed by two parallel lines cut by a transversal, the angles can be on either side, but the same side of the transversal (outside parallel lines) and their measure adds up to 180 degrees

Alternate exterior angles

when eight angles are formed by two parallel lines cut by a transversal, the angles on the alternating sides of the transversal (outside the parallel lines) and they have the same measure

Euclidean plane

a traditional plane, no coordinates. A flat two-dimensional surface that extends infinitely in all directions.

Coordinate plane

a two-dimensional surface formed by two perpendicular number lines (x-axis and y-axis) that intersect at point called the origin (0,0)

Congruent

If two geometric figures (points, rays, lines, segments, angles triangles, polygons etc.) have the same shape and size one of them could be placed on top of the other simply by moving it