Do Now 10/2/09In the diagram below, AB and CD intersect at E, (m) Angle AEC = 6x -20 and the (m) Angle

BED is 4x + 10. Find the value of x.

(6x -20) (4x + 10)

A

E

B

D

C

AnswerSpecial Angle Relationship Property: Vertical

AnglesTherefore,

6x-20 = 4x+10+20 = +206x = 4x +30

-4x = -4x2x = 30x = 15

Theorems involving Pairs of AnglesThm: 4.3 If two angles are complements of the

same angle, then they are congruent.

Thm: 4.4 If two angles are congruent, then their complements are congruent.

Thm: 4.5 If two angles are supplements of the same angle, then they are congruent.

Thm: 4.6 If two angles are congruent, then their supplements are congruent.