13. b
a
∠A + ∠B = 180º
∠B = 180º - 50º
= 130º
∠A and ∠B are known as adjacent angles on a straight line
The sum of adjacent angles on a straight line is 180º
17. Vertically opposite angles
D
A
E
B
C
∠AED = ∠CEB and ∠AEC = ∠BED
The pairs of equal angles are known as vertically opposite angles
Vertically opposite angles are equal
18. D
150º
A
30º
30º E
150º B
C
∠AEC = ∠BED = 30º
∠AED = 180º - ∠AEC
= 180º - 30º
= 150º
19. Parallel Lines
A B
AB // CD
C D
AB and CD not parallel to EF
E
F
AB // CD // GH
G H
J EF not parallel to IJ
I
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