Section 4-5
The congruent sides of an isosceles triangle are
its legs.
 The third side is the base.
 The two congruent legs form the vertex angle.
 The other two angles are the base angles.

 If
two sides of a triangle are congruent, then
the angles opposite those sides are
congruent.
 If AB  CB then A  C
 If
two angles of a triangle are congruent,
then the sides opposite those angles are
congruent.
 If A  C then AB  CB
 If
a line bisects the vertex angle of an
isosceles triangle, then the line is also the
perpendicular bisector of the base.
 Corollary

If a triangle is equilateral, then the triangle is
equiangular.
 Corollary

to Theorem 4-3
to Theorem 4-4
If a triangle is equiangular, then the triangle is
equilateral.
 Complete
 1.
 2.
 3.
 4.
each statement.
DBC  ?
 CDB
BED  ?___
FED  __?___  DFE
AB  _____  _______
 Solve
for x and y.
 A.
x = 180-115
x = 65
y = 180-65-65
y = 50
 B.
x + 5 = 60
x = 55
y – 10 = 60
y = 70
 Pg
254 #6-12, 16-19
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