Triangles by angle:
Acute- All angles are less than 90 degrees (none at 90 or higher)
Obtuse- At least one angle is greater than 90 degrees (No angle=90 and two angles are less than 90 degrees)
Right- One angle is exactly 90 degrees
Triangles by side length:
Scalene- No two sides are of the same length
Isosceles- Two sides are of the same length
Equilateral- Three sides are of the same length
Other definitions:
Acute angle- less than 90 degrees
Obtuse angle- greater than 90 degrees
Right angle- exactly 90 degrees
Point- undefined term/ unseen/ can be represented by a dot
Line- undefined term/ straight, contains an infinite amount of points in two directions/ no thickness/ line AB goes
through points A and B/ Line AB or
Plane- an undefined term/ a flat service that extends in all directions
Ray- consist of an initial point and goes in one direction infinitely. Undefined term. Ray AB starts at A and goes through
point B/ Ray AB or
Endpoints- the points at the beginning and end of a segment
Line segment or Segment- a measurable line with a start and stop. Line AB starts at A and ends at B. Line AB or
Vertex- where two lines intersect or an intersection of two rays or two segments for examples. An angle has one vertex.
A square has four vertices (plural for vertex). A pyramid has a vertex at the top where three lines meet at a point.
Vertical angles- when two lines cross, the angles across from each other are congruent and their measures are equal.
Linear angles- are two angles that lie on a line and are supplementary and adjacent.
Supplementary angles- Two angles that add up to 180 degrees
Complementary angles- Two angles that add up to 90 degrees
Altitude of triangle- a segment from a vertex that is perpendicular to the opposite side or to the line containing the
opposite side (that is the book for you). My definition- The height of the triangle from its base (a measurable segment);
this segment is the shortest distance so it is perpendicular to the base. / there are three for each triangle
Median of a triangle- a segment whose endpoints are a vertex of the triangle and the midpoint of the opposite side.
There are three for each triangle.
Perpendicular bisector- A perpendicular line that splits a segment into two equal points; goes through the midpoint.
Midpoint- the one and only point in the middle of a segment.
Angle bisector- a ray or segment that splits an angle into two equal angles.
Concurrent- two or more lines or segments that intersect at a single point
Point of concurrency- the point where two or more lines meet together (and yes, this is a vertex too).
Incenter of triangle- three angle bisectors meet at point of concurrency- a circle can be inscribed (touches all the sides)
from this point.
Circumcenter of a triangle- three perpendicular bisectors meet a point of concurrency. A circle can be drawn that
circumscribes (touches all the vertices) the triangle at this point.
Orthocenter- the three altitudes of a triangle meet at this point of concurrency
Centroid- the three medians of a triangle meet at this point of concurrency. This is the center of gravity for a triangle.
The centroid is 2/3rds of the distance from each vertex to the midpoint of the opposite side.