The terms point, line, and plane are referred to as undefined. When you write the definition of these terms, you have to rely on other terms that need defining.
Point- In general, a point is a location. Because points have no size, you can say they have no dimension.
Line- a "stream" of points that has no width or depth. You can also think of a line as points lined up next to each other that go on forever in opposite directions. Because you can measure the distance between points, lines have one dimension: length.
Collinear- Points on the same line.
Noncollinear- Points not on the same line.
Plane- a flat surface that extends indefinitely in all directions. Because two measurements can be made on a plane—the distance between two points on a line and the distance from a line to a point not on that line—planes have two dimensions: length and width.
Line Segment- A line segment is a portion of a line with two endpoints. Every point between and including the endpoints is part of the line segment.
Angle- a figure consisting of two noncollinear rays or segments with a common endpoint
Ray- part of a line that has one endpoint and continues in one direction infinitely.
Postulates- statements that mathematicians assume to be true without any proof to support them.
Ex: In the English alphabet, A comes before B. In math, you could draw a line through any two distinct points given.
Theorem- information that seem true but must be proven (like solving a mystery) using the postulates.
Ex: The Pythagorean theorem is proven true by using mathematical equations and postulates.
Points postulate- There is exactly one line through any two points. When given two points, you could draw a line through them.
Intersecting lines postulate- When two lines intersect, they intersect at exactly one point. Otherwise, it’s not a true line, or it’s the same line.
Intersecting planes postulate- When two planes intersect, they