Angles & Triangles

1. https://www.mathsisfun.com/triangle.html
2. http://mathworld.wolfram.com/Triangle.html
3. http://www.factmonster.com/ipka/A0876325.html
4. http://www.coolmath.com/reference/triangles-types
5. https://www.khanacademy.org/math/geometry/triangle-properties
6. http://www.learnhive.net/learn/cbse-grade-7/mathematics/triangle-and-its-properties
7. http://www.learnhive.net/learn/cbse-grade-7/mathematics/congruence-of-triangles
8. https://www.mathsisfun.com/definitions/supplementary-angles.html