### Geometry for Elementary School/Lines - Wikibooks, open books for an open world

Well, unless you're high, you're a mathematician, or you're a high mathematician, two parallel lines don't intersect. A notable exception is in. The point where they cross or touch is called the point of intersection. Perpendicular lines, segments, or rays: Lines, segments, or rays that intersect at right angles (90° angles) are perpendicular. Take two pencils or pens, one in each hand. Adjacent Angle - Angles that share a vertex, one side, and no interior points. Alternate That is, they lie between the two lines that intersect with the transversal.

A rectangle is a four sided figure where all four angles are right angles. A rhombus is a four sided figure where all four sides have the same length. A tirangle is an isosceles triangle if two of its sides have the same length. A triangle is an equilateral triangle if all three sides have the same length. A median of a triangle is a line segment from one verted to the midpoint of the opposite side.

### Intersecting Lines | Intersecting Lines Examples | [email protected]

An altitude of a triangle is a line segment from one vertex perpendicular to the opposite side The point where the perpendicular bisectors of the three sides of a triangle meet is called the circumcenter of the triangle. The circle which goes through all three points of a circle is called the circumscribed circle or circumcircle. The point where the three angle bisectors of a triangle meet is called the incenter of the triangle.

The circle to which all three sides of a triangle are tangent is called the inscribed circle or incircle. The point where the three medians of a triangle meet is called its centroid or center of gravity. The point where the three altitudes of a triangle meet is called the orthocenter of the triangle.

The Euler line of a triangle goes through the circumcenterthe centroidand the orthocenter. The 9 point circle is centered at the midpoint of the Euler line and goes through the midpoints of the three sides, the feet of the altitudes, and the midpoints of the line segments between the orthocenter and the vertices of the triangle. A regular polygon is one where all the sides have the same length and all of the angles are the same size. The point where all of the angle bisectors meet in a regular polygon is called the center of the polygon.

Coordinates - A set of two numbers that indicate where a point is on a graph.

## Intersecting Lines

The first number indicates the x-axis and the second number the y-axis. Other names include ordered pair and numbered pair. Coplanar lines - Two or more lines that are on the same plane or flat surface.

Diameter - A line segment that passes through the center of a circle with each end point being on the circumference.

## Lines, Rays, and Angles

Endpoint - The point at the end of a line segment or ray. Horizontal - A flat or level line or plane that is perpendicular to the vertical.

Intersecting lines - Two or more lines that meet at a point are intersecting. Line - A straight object that is infinitely long and thin. It is only in one dimension. Line segment - A portion of a line with two endpoints.

Midpoint - The point of a line segment that is the same distance from both endpoints.

Noncollinear points - A set of three points that are not located on the same line. Number pair - Two numbers that represent a point on a graph, also called the coordinates. Ordinate - The vertical line, or y-axis, of a graph.

Origin - The origin is the point where the X and Y axis intersect on a graph.