• Triangle definition
• Interior angles
• Exterior angles
• Exterior angle theorem
• Hypotenuse of a right triangle
• Medians of a triangle
• Altitudes of a triangle
• Midsegment of a triangle
• Triangle Inequality Theorem
• Converse of Triangle Inequality Theorem
• Side / angle relationships

Triangle Perimeter and Area

• Perimeter of a triangle
• Area by the "half base times height" method
• Area using Heron's formula
• Area of an equilateral triangle
• Area by the "side angle side" method
• Area of a triangle with fixed perimeter

Types of triangle

• Acute
• Obtuse
• Isosceles
• Scalene
• Equilateral
• Equiangular
• Right triangle

Special right triangles

• 45° 45° 90° right triangle
• 30° 60° 90° right triangle
• Pythagorean triples
• The 3:4:5 pythagorean triple

Solving the triangle

• Introduction. What does 'solving' a triangle mean?
• The Pythagorean Theorem and its converse
• A graphical proof of the Pythagorean Theorem
• Law of Sines
• Law of Cosines

Congruent triangles

• See Congruence Chapter

The Centers of a Triangle
(Points of concurrency)

• Triangle centers - an overview
• Centroid
• Circumcenter
• Incenter
• Orthocenter
• Euler line

The Circles of a Triangle

• Incircle
• Circumcircle

Triangle problems

• Quiz: Test your knowledge of triangle types
• The "Many Triangles" problem
• The "Many Triangles II" problem
• The "Ball Box" problem
• The "Three Satellites" problem