Download Honors Geometry Section 4.4 Isosceles Triangle Theorem

Geometry Section 4.6
Isosceles Triangle Theorem
Goals for today:
1. Identify the parts of an isosceles triangle.
2. Learn and apply the Isosceles Triangle
Theorem and its converse.
Recall that an isosceles is a triangle with
two congruent sides
_________________.
The congruent sides are called the ____
legs
and the noncongruent side is called
base The angle formed by the two
the_____.
vertex angle while the
legs is called the ___________
two angles at each end of the base are
called ___________.
base angles
Theorem 4.6
Isosceles Triangle Theorem (ITT)
If two sides of a triangle are
congruent, then the angles
opposite those sides are
congruent.
A  C
Theorem 4.7 Converse of the
Isosceles Triangle Theorem (ITTC)
If two angles of a triangle are
congruent, then the sides opposite
those angles are congruent.
Examples: Solve for x.
2 x  11  64  64  180
2 x  117  180
2 x  63
x  31.5
180  38  142
142 / 2  71
180  71  109
180 / 3  60
6 x  11  8 x  12
23  2 x
x  11.5
3 x  6  5 x  15
21  2 x
x  10.5
Classify ABC according to its angles and sides.
A
180  45  135 / 2  67.5
acute isosceles
B
450
C