1. 3.5 Parallel lines and Triangles

2. Parallel lines help with triangle postulates.
55°
87°
38°

3. Triangle Sum Theorem
All interior angles of a triangle add to 180°.

4. Ex 1 X=
87°
38° x°

5. Ex 2
X=____ ∠A=_____ ∠B=_____ A
x+3°
22°
x°+11 C B

6. Ex 3
If all three interior angles of a triangle have the ratio1:2:3 Draw the picture . Then find all angles.

7. Triangles have exterior angles.
Angle M is an exterior angle. m

8. Exterior Angle Theorem
Any exterior angle is equal to the sum of the non-connected interior angles.
∠1+ ∠2= ∠3 3 1 2

9. Ex 4
Find angle M. and x x
65° m
75°

10. H.W pg 175
1-5 odd, 9-13 all, 16-18all all, 29-30