Chapter 2 of 10All chapters
Chapter 2 of 10
Triangles
Three sides, endless consequences.
Kinds and rules
Angles always add to 180. Equilateral has three equal sides, isosceles two, scalene none. An exterior angle equals the sum of the two opposite interior angles.
- Any two sides must add to more than the third, or the triangle cannot close.
- The largest angle sits opposite the longest side.
Right angles
Pythagoras relates the three sides: the square on the hypotenuse equals the sum of the other two squares. It is the single most used result in practical geometry.