1. Basic Theorems of Triangles Sophomore Geometry By: Shannon Manzella

2. Interior Angles Theorem In a Triangle, the Interior Angles will always add to be 180° – The Interior Angles are the inside angles between adjacent sides of a rectilinear figure.

3. Example A

4. Base Angles Theorem If the sides of a triangle are congruent ( like in an Isosceles triangle) then the angles opposite these sides are congruent. – Two angles are congruent if they have the value and size. Leg A Leg B Base Angle B Base Angle A

5. Example B

6. Example C

7. The Midpoint Theorem The segment joining the midpoints of two sides of a triangle is parallel to the third side and half as long as the third side. – The Midpoint of a line segment is the point that is halfway between the endpoints of the line segment.

8. Example D

9. Example E

10. Cites http://www.toxel.com/wp- content/uploads/2012/12/meltedcrayon08.jp g http://www.toxel.com/wp- content/uploads/2012/12/meltedcrayon08.jp g http://www.mathwarehouse.com/geometry/t riangles/ http://www.mathwarehouse.com/geometry/t riangles/ http://www.basic-mathematics.com/base- angles-theorem.html http://www.basic-mathematics.com/base- angles-theorem.html http://www.cliffsnotes.com/math/geometry/p olygons/the-midpoint-theorem http://www.cliffsnotes.com/math/geometry/p olygons/the-midpoint-theorem