What is the reason for Step 3 in the proof below?

Question

Linear Pair Postulate

Angle Addition Postulate

Subtraction Property of Equality

Addition Property of Equality

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Answer 1 · 2017-12-08T15:56:11

Linear pair postulate: angles in a straight line sum to #180^o#

In a straight line, the sum of the angles add up to 180; this is known as the "Linear pair postulate"

Sorry about my skills with MS Paint, or lack thereof

Since #m/_1# and #m/_2# are in a straight line, their angles must sum to 180. This is the same with #m/_2# and #m/_3#. Therefore,

#m/_1+m/_2=180^o#
#m/_2+m/_3=180^o#