Download 4.3 Notes - Scott County Schools

Geometry 4.3 Notes
LT 4.3- I can find the measures of interior and exterior angles of triangles, and I can apply theorems
about the interior and exterior angles of triangles.
Triangle Sum Theorem: The sum of the measures of angles in a triangle is 180°.
m∠A+m∠B+m∠C=180
Y
Ex.
A
C
B
12°
62°
W
40°
Z
X
Find m∠XYZ
Find m∠WXY
Find m∠YWZ
Proven: The two acute angles if a right triangle are complementary.
Proven: The angles of an equiangular triangle measure 60°.
Exterior Angle Theorem
The neasure of an exterior angle of a triangle is equal to the sum of the measures of the remote
interior angles.
(2x+3)°
B
Find m∠B
Ex.
15°
(5x+60)°
A
C
D
Third Angles Theorem
If two angles of one triangle are congruent to two angles of another triangle, the third pair of angles
are congruent.
J
K
(4y)°
Ex:
F
(6y-40)°
G
H
I
Find ∠J and ∠K