all vocab and random stuff here and there from chapters 1-6.

### line

extends in 1 dimension

-usually represented by a straight line with arrows at each end

-has length

-never ends (infinite)

### plane

extends in 2 dimensions (has length and width), usually represented by a shape that looks like a wall or a table top

-also infinite

### opposite rays

have the same initial point, but go in opposite directions

-when looked at together, make line

### points of intersection

2 or more geometric figures intersect if they have 1 or more points in common

### vertical angles

two angles whose sides form 2 pairs of opposite rays (2 intersecting lines)

-shared vertex in middle

### supplementary

two angles whose measures add to exactly 180 degrees

-can be adjacent or non adjacent

-all linear pairs are supplementary

### line perpendicular to a plane

that intersects a plane at a point so that it forms a right angle with every line in that plane

### biconditional statements

contain the phrase "if and only if" (Or IFF); same as writing a conditional statement and its converse together

### deductive reasoning

uses facts, definitions, and accepted properties in a logical order to write a logical argument

### flow proof

uses arrows to show the flow of logical argument (reasons are usually written below the statements)

### vertex angle

in an isosceles triangle: angle opposite to the base; sides are the 2 congruent legs of the triangle

### coordinate proof

involves placing a geometric figure in the coordinate plane

-then we use distance and midpoint formulas long with postulates, theorems, etc, to prove statements

### perpendicular bisector of a triangle

a line, ray, or segment that is perpendicular to a side of the triangle at the midpoint of the side

-every triangle has 3

-all intersect at one point

### incenter

point of concurrency of angle bisectors

-always inside the triangle

-equidistant from all 3 sides of the triangle

### median of a triangle

a segment whose endpoints are vertex of a triangle and the midpoint of the opposite side

-every triangle has 3

-are concurrent

### centroid

point of concurrency of medians of a triangle

-always inside the triangle

-balance point for the triangle

### altitude of a triangle

perpendicular segment from a vertex to the opposite side (or the line containing the opposite side)

-every triangle has 3

-are concurrent

### orthocenter

point of concurrency of altitude of a triangle

-acute triangle: inside

-right triangle: on the triangle, vertex of the right angle

-obtuse triangle: outside

### indirect proof

prove a statement is true by first assuming that its opposite is true

-if assumption leads to an impossibility, then the original must be truel

### polygon

a plane figure formed by 3 or more segments so that each segment intersects exactly 2 others at each end point

-no curves, gaps, overlaps, or criss crosses

### square

all 4 angles and all 4 sides are congruent

-equilateral and equiangular parallelogram (REGULAR)