Equiangular Triangle

equilateral triangle: a three-sided regular polygon

Scalene Triangle

a triangle with no two sides of equal length

Isosceles Triangle

a triangle with two equal sides.

Legs (of a right triangle)

In a right triangle, the sides opposite to the acute angles are called the Legs of a Triangle.

Obtuse Triangle

A triangle where one of the internal angles is obtuse (greater than 90 degrees).

Example

Real life example

Acute Triangle

a triangle whose interior angles are all acute

Regular Polygon

A polygon that has all sides equal and all interior angles equal

Regular

Real life example

Altitude (of a triangle)

 in the altitude of a triangle, the altitude refers to the perpendicular distance from the vertex to the opposide. In the image, note that the altitude is AD. AD is the altitude from A to BC.

Alternate Exterior Angles

When two parallel lines are cut by a transversal, the two pairs of angles on opposite sides of the transversal and outside the parallel lines, and the angles in each pair are congruent.

Example

Real life example

CPCTC

Corresponding parts of congruent triangles are congruent

Line Segment

A straight line which links two points without extending beyond them.

Ray

A line which starts at a point with given coordinates, and goes off in a particular direction to infinity, possibly through a second point.

Complementary Angles

Either of two angles whose sum is 90°.

Midpoint

The exact middle point.

Angle Bisector

A line which cuts an angle into two equal halves.