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l. • C. • B. • D. • F. • E. M. Building Blocks of Geometry. Three “undefined” terms are the building blocks of Geometry We can agree on their meaning, but there is no precise mathematical definition A point has no dimension Represented by a dot Named with a single letter
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l • C • B • D • F • E M Building Blocks of Geometry • Three “undefined” terms are the building blocks of Geometry • We can agree on their meaning, but there is no precise mathematical definition • A point has no dimension • Represented by a dot • Named with a single letter • A line has one dimension, extending both ways with no end • Represented by a line with arrowheads on both ends • Named with a script letter, line l, or by listing two points beneath a line symbol, BC • A plane has two dimensions, a flat surface extending in all directions • Represented by a parallelogram • Named by a letter, plane M, or by three points in the plane, plane DEF • A ↔
• C • B Building Blocks of Geometry • A postulate is a statement that is accepted without proof • There are about a dozen postulates that form the basis of Geometry Postulate 1 Two Points Determine a Line Through any two points there is exactly one line Postulate 2 Three Points Determine a Plane Through any three points not on the same line there is exactly one plane • Collinear points are points that lie on the same line • Coplanar points are points that lie on the same plane • Coplanar lines are lines that lie on the same plane • A
• Q • P • T • S • R Building Blocks of Geometry • A segment consists of two points on a line and all points that lie between them • A segment is named using the two endpoints, PQor QP • A ray consists of one point on a line and all points that are on one side of the endpoint • A ray is named using the endpoint and any point on the ray, RSor RT • The endpoint must be listed first • The ray shown cannot be named SR or ST ─ ─ → → → →
