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2015-04-02 Geometry
“Factsheet for Interior and Exterior Angles of a Polygon
and Isoceles Triangles”
The sum of the measures of the interior angles
of a polygon of n sides = 180 (n-2)°
Measures of the Exterior Angles of a Polygon with N Sides
The measures of the exterior angles = 180n – the measures of the interior angles
= 180n – 180 (n-2)°
= 180n - (180n – 360)
= 360°
The sum of the exterior angles of a polygon is always 360°
Isosceles Triangles: Triangles with two equal sides.
Proof that the base angles of an isosceles triangle are equal (congruent):
Statements
Reasons
Triangle ABC
Given
AC = BC
Given
Draw CD to midpoint of AB
AD = DB
CD = CD
Triangle ACD
<A
<B
You can draw a line between 2
points
A midpoint divides a line segment
in half
Reflexive property
Triangle DCB
SSS
Corresponding parts of congruent
triangles are congruent.