Angle Addition Postulate
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Definition of Angle Addition Postulate
Angle Addition Postulate states that if a point S lies in the interior of ∠PQR, then ∠PQS + ∠SQR = ∠PQR.
More about Angle Addition Postulate
 If the sum of the two angles measure up to 90^{0}, then the angles are called to be 'complementary angles'.
 If the sum of the two angles measure up to 180^{0}, then the angles are called to be 'supplementary angles'.
 The angles sharing a common side are called as 'adjacent angles'.
Examples of Angle Addition Postulate

According to angle addition postulate, m∠DAC + m∠CAB = m∠DAB. So, m∠DAB = 35^{0}+ 30^{0} = 65^{0}.
Video Examples: Angle Addition Postulate  Geometry Help
Solved Example on Angle Addition Postulate
Ques:
Find m∠CAB. [Given ∠DAB = 64^{0} and ∠DAC = 53^{0}.]
Choices:
A. 28B. 15
C. 11
D. 117
Correct Answer: C
Solution:

Step 1: m∠DAC + m∠CAB = m∠DAB [Angle Addition Postulate.]
Step 2: m∠CAB = m∠DAB  m∠DAC
Step 3: m∠CAB = 64  53 [Substitute.]
Step 4: m∠CAB = 11 [Add.]
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