1. Classifying Triangles by ANGLES
Geometry/Trig Name: _________________________
Introduction to Triangles Date: __________________________
ACUTE
OBTUSE
Classifying Triangles by ANGLES
RIGHT
EQUIANGULAR
SCALENE
ISOSCELSES
EQUILATERAL
Classifying Triangles by SIDES

2. Statements Reasons Statements Reasons
Vertices of DABC: _________________
Sides of DABC: ___________________
Angles of DABC: ___________________ B A C
Theorem: the three interior angles of a triangle sum to _________.
x = ______
mÐA = _______
mÐB = _______
mÐC = _______
Example 1:
mÐA = 56
mÐB = ____
mÐC = 82
Example 2:
mÐA = 3x + 5
mÐB = x - 4
mÐC = 2x + 11
Given: ___________________________
Prove: ___________________________
Statements
Reasons 1. 2. 3. 4. 5. 6.
Corollary: The acute angles in a right triangle are ____________________.
Given: ________________________
Prove: ________________________
Statements
Reasons 1. 2. 3. 4. 5. 6.

3. Identify the remote interior angles for each exterior angle.
Exterior Angle of a Triangle: An angle that forms a ____________________ with an interior angle of a triangle. In DABC, ____________, is an exterior angle.
Remote Interior Angles: the two angles of the triangle that are not ____________ to a specific exterior angle.
With respect to exterior Ð4, the remote interior angles are ___________ and _____________.
Identify the remote interior angles for each exterior angle.
Ð2 _______________ Ð6 ________________
Ð1 _______________ Ð5 ________________
Ð7 & Ð9 are remote interior angles for the exterior angles ________
Theorem: The exterior angle is equal to the sum of the two remote interior angles.
Given: DABC
Prove: mÐ1 + mÐ2 = mÐ4
Statements
Reasons 1. 2. 3. 4. 5.
Given: ________________________________
x = ____, mÐ1 = ____, mÐ2 = ____, mÐ3 = ____, mÐ4 = ____, mÐ5 = ____
Given: ________________________________
x = ____, mÐ1 = ____, mÐ2 = ____, mÐ3 = ____, mÐ4 = ____, mÐ5 = ____

4. A triangle with three congruent sides.
Match the definitions with the correct vocab term. Then turn to page 93 and copy down the diagrams for each.
A triangle one right angle (measures exactly 90 degrees). The other two angles are acute and are complementary.
A triangle with three congruent sides.
A triangle with three acute angles (all three angle measures are below 90 degrees).
A triangle with NO congruent sides.
A triangle with three congruent angles. The three angles all measure 60 degrees. These triangles are also classified as acute.
A triangle with two congruent sides.
A triangle with one obtuse angle (a angle that measures over 90 and under 180). The other two angles are acute.