-Theorem of the sum of triangle internal angles: the sum of triangle internal angles is equal to 180.
Pythagorean theorem: the square of the hypotenuse of a right triangle is equal to the sum of the squares of the two waists.
-Sine theorem: In any triangle ABC, there is a/sinA=b/sinB=c/sinC.
-Cosine Theorem: In any triangle ABC, there are a_=b_+c_-2bccosA, b_=a_+c_-2accosB, and c_=a_+b_-2abcosC.
-similar triangles's theorem: Two triangles are similar if their three sides are proportional.
-Proportional theorem of parallel segments: If a straight line intersects two parallel lines, the distance between them is proportional to the distance between the two parallel lines.