Since we are upgrading our website, we have decided to compress all the Geometry proofs into one single post. Below are the contents of this post : Angles: The sum of the angles of any triangle is 180 ° The sum of the inner angles of any polygon Lines, Length & Distance: Pythagoras Theorem Sine, Cosine, Tangent specific value with specific angles Areas: Area of an obtuse triangle Area of a trapezoid The sum of the angles of any triangle is 180° ∵AB//CD ∴∠CAB + ∠ACD = 180° ∴∠C