Geometry Definitions

Front 1

Open Line Segment

Back 1

AB˚={P:A*P*B}

Front 2

Lie on the same side

Back 2

2 points are said to lie on the same side iff AB(intersect)l = ø or if A = B

Front 3

Lie Between

Back 3

A ray AD is said to lie between two rays AB and AC iff AB and AC are not opposite rays and D is interior to alpha = ray(AB) U ray(AC)

Front 4

Half-Plane

Back 4

If in plane X, A is a point not on L then

H = {C in X: A, C lie on same side of l)

Front 5

Ray

Back 5

Suppose A = B

Ray(AB) = {P: P is in AB or A*B*P)

Front 6

Interior Angle of ∆ABC

Back 6

alpha = ray(AB) U ray(AC)
beta = ray(BA) U ray (BC)
gama = ray (CA) U ray (CB)

Front 7

exterior/lie outside

Back 7

A point is said to lie outside if it is not interior or lie in an angle alpha

Front 8

Interior of ∆ABC

Back 8

Int(ABC) = {P:P is interior to alpha, beta, and gama}

Front 9

Exterior of ∆ABC

Back 9

set of points P such that P is not interior to, nor on ∆ABC

Front 10

Opposite Ray

Back 10

If r = ray(AB)

opp(AB) = {P: P*A*B or P = A}

Front 11

Vertex

Back 11

Points on a triangle

In the Angle BAC = ray(AB) U ray(AC), A is the vertex

Front 12

A point lying interior or inside

Back 12

P lies inside alpha = angle(BAC) iff B,P lie on same side of ray(AC) and CP lie on same side as ray(AB)

Front 13

∆ABC

Back 13

ABC = AB U AC U BC

Front 14

Affline Plane

Back 14

A plane satisfying all 3 incidences and the parallel postulate

Front 15

Angle

Back 15

A union of rays emanating from one point

Front 16

Line Segment

Back 16

Suppose A≠B

AB = {P:P=A, P=B or A*P*B

Front 17

Parallel

Back 17

Lines l and m are said to be parallel when l intersect m = ø

Front 18

Concurrent

Back 18

Lines are said to be concurrent when they all intersect at a certain point P

Front 19

Collinear

Back 19

Points are said to be collinear iff they all lie on the same line