# 1st Period Androli Math

## 21 terms

### Point

A placeholder in space; 1 dimensional

### Line

An infinite set of points extending in both directions for infinity

### Plane

Two-Dimensional infinite set of points

### Line segment

a part of a line with two endpoints

### ray

a straight line extending from a point

### angle

two rays with a common endpoint

common endpoint

### triangle

the union of three line segments

### union

everything contained in both sets whether or not they are common

### intersect

the only points common to both sets

### acute angle

an angle less than 90 degrees but more than 0 degrees

### obtuse angle

an angle between 90 and 180 degrees

### right angle

the 90 degree angle between two perpendicular lines

### straight angle

an angle of 180 degrees

### collinear points

Points that lie on the same line

### betweenness

given two numbers, another number is said to be between those two numbers if it is greater than the first but less than the second

### triangle inequality

The sum of the lengths of any 2 sides of a triangle is greater than the length of the third side.

### midpoint

the point where a line segment is bisected

### postulates

statements that we accept without proof

has to be true

### transitive property of equality

if a=b and b=c, then a=c