Download Theorem 4

Theorem 4.9: If 2 sides of a triangle are congruent
then the angles opposite those sides are congruent.
(Base angles of an isosceles triangle are congruent)
B
Proof:
Given: ABC with AB  BC
Prove: A  C
A
C
D
Given: AB  CB  BD
ACB  BCD
C
Prove: D  A
B
A
Statements
Reasons
Theorem 4.10: If two angles of a triangle are
congruent, then the sides opposite those angles are
congruent.
Corollary 4.3: A triangle is equilateral iff it is
equiangular.
Corollary 4.4: Each angle of an equilateral triangle
has a measure of 60 degrees.