Proving that lines are (and aren’t)

parallel

Corresponding Angles Postulate

• Two lines are cut by a transversal• if the two lines are parallel then the

corresponding angles are equal.• What would the converse of this statement

be?

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If the corresponding angles are equal then the two lines are parallel

Find a value of x that makes the m//n

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Other ways to prove //

• What else did we prove on Friday?• Could you take the converse of those as well?

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If the corresponding angles are equal then the two lines are parallel

Other ways to prove //

• What else did we prove on Friday?• Could you take the converse of those as well?• Do you think they would be true as well?

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You try• Assuming that two lines are cut by a

transversal• Write your notes from Friday in the form of a

conditional• Take the converse of that and discuss with

your neighbors if you think that will be true.• In 10 minutes I am going to pull 3 names to

discuss them.• If the corresponding angles are equal then the

two lines are parallel.

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Summary

• There are at least 4 ways to prove lines are parallel (CA, AIA, AEA & CIA)– List them out (with pictures)

• Things to think about– could you use these relationships to setup

equations?– How many different angle measures would you

see if two parallel lines were cut by two parallel transversals (like on the first page)