1. Use isosceles and equilateral triangles
Section 4-8

2. Isosceles Triangles Base angle Base angle BASE ANGLE THEOREM…
If two sides of a triangle are congruent, then the base angles are also congruent.
Base angles are the angles at the ends of the 2 congruent segments, or opposite of the congruent sides.
So, in the diagram angles B and C are congruent.
There are two congruent sides in an isosceles triangle and two congruent angles.
Base angle
Base angle

3. Converse to the Base Angles Theorem
If two angles in a triangle are congruent, then the triangle is an isosceles triangle.
That means that the 2 sides of the triangles are also congruent.

4. Equilateral Triangles
All of the sides and angles should be congruent.
The angles in an equilateral triangle always equal 60o.
If it is an equilateral triangle, then it is also equiangular.
Converse of Equilateral Triangle Theorem
If the triangle is equiangular, then the triangle is equilateral.

5. Example 1 This is an isosceles triangle, so the 2 sides are congruent…

6. Example 2
This is an isosceles triangle, so the 2 angles are congruent…
9x = 72
x = 8

7. Example 3
x + x = 180
2x = 180
2x = 78
x = 39

8. Example 4 The sum of the interior angles is 180… x + 7 = 55 x = 48
y = 180
110 + y = 180
y = 170

9. Example 5
Triangle DEG is equilateral, therefore the angles are each 60 degrees. X=60

10. What are all of the missing angles?

11. Example 6 GIVEN ANGLE G IS CONGRUENT TO ANGLE J
TRIANGLE FGH IS CONGRUENT TO TRIANGLE FJI
CPCTC

12. VERTICAL ANGLE THEOREM
GIVEN
GIVEN
VERTICAL ANGLE THEOREM
TRIANGLE AEC IS CONGRUENT TO TRIANGLE BEC
CPCTC
BASE ANGLE THEOREM

13. Assignment #46 Page 267 #4-10 even #14-20 even #11 #21
DUE TOMORROW!! I WILL COLLECT IT AT THE BEGINNING OF THE PERIOD!
Assignment #46 Page 267 #4-10 even #14-20 even #11 #21
PRINT THE CH. 4 TEST STUDY GUIDE!
CLASS THAT BRINGS THE MOST GETS CANDY!!