1. Mr. Schaab’s Geometry Class Our Lady of Providence Jr.-Sr. High School 2014-2015

2.  A triangle is a polygon with three sides.  A triangle with vertices (corners) A, B, and C is called “triangle ABC” or “ △ ABC.”

3.  A triangle’s interior angles are the three angles contained within the boundaries of the triangle.  The exterior angles of a triangle are the angles formed when the sides of the triangle are extended. They always lie outside the triangle.

5.  If two sides of a triangle are congruent, then the angles opposite those sides are also congruent.  Recall Unit 2 about conditional statements: What is the converse of this statement?  If angles opposite two sides of a triangle are congruent, then those sides are also congruent.

6.  Materials:  1 piece loose leaf paper  Ruler with straight edge  Pencil  Instructions: 1. Select any two lines on paper that are at least 10 lines apart. Use straight-edge and pencil to darken those lines. 2. Mark a point near the center of the paper that is exactly halfway between the top and bottom lines. 3. Use straight-edge to draw two distinct lines that intersect the two horizontal lines and the point you just made. 4. You should now have two triangles on your paper. Label the vertices of each triangle. (Use a different letter for each vertex.)

7.  Congruent Figures – If two geometric figures are congruent, then all the parts of one figure are congruent to the corresponding parts of the other figure.  In the diagram, ∠ P and ∠ L are corresponding angles, and JK and QR are corresponding sides.

8. When writing a congruence statement for triangles, order is important! Corresponding vertices need to be written in the same order for both triangles. ▲QPR ≅ _________ ▲RPQ ≅ _________ ▲PRQ ≅ _________ ▲JLK ▲KLJ ▲LKJ

9.  If two angles of one triangle are congruent to two angles of another triangle, then the third angles are also congruent.  In the diagram, the unlabeled angles must be congruent. What is the measure of both unlabeled angles?  73°