Complementary angles
Supplementary angles
Angles around a point
Alternate angles (parallel lines)
Corresponding angles (parallel lines)
Co-interior angles (parallel lines)
Congruence of triangles (SSS, SAS, AAS, RHS)
Isosceles triangle theorem (mid point of base at right angles)
Radius Tangent theorem proof
https://www.khanacademy.org/math/geometry/hs-geo-circles/hs-geo-tangents/v/proving-radius-is-perpendicular-to-tangent-line