Remote Interior Angle Theorem
editThe measure of the exterior angle of a triangle is equal to the sum of the measures of the other two remote interior angles.
Given: In ∆ABC, angle ACD is the exterior angle.
To Prove: m ACD=m ABC+m BAC
Proof:
Hence, proved.
Isosceles Triangle Theorem
editIf two sides of a triangle are congruent, then the angles opposite to them are congruent.
Given: In ∆ABC, Side AB Side AC.
To Prove: ABC ACB.
Construction: Draw the bisector of BAC, intersecting Side BC in point D.
Proof:
Hence, proved.