Courtney H.

asked • 03/10/17

# Given: triangle ABC. Prove: m<1 + m<2 + m<3 = 180

Translate ΔABC by vector AB  to form straight <ABB'  along the vector.  The isometric properties of translation preserve _________, thus m<1 = m<B'BC'.  Since <ABB'  is a straight angle, we know that m<2 + m<CBC' + m<B'BC' = __________°.  Translation also preserve ________,  there for ensuring that line AC parallel to line BC'. Since line AC parallel to line BC', m<3 = m<CBC' because alternate ________ angles are congruent. By making two ________ into the  straight angle relationship of  m<2 + m<CBC' + m<B'BC' = 180º we  arrive at the proof that m<1 + m<2 + m<3 = 180º.

## 1 Expert Answer

By:

Michael J. answered • 03/10/17

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Effective High School STEM Tutor & CUNY Math Peer Leader

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