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Lesson 2-5: Proving Lines Parallel 1

Lesson 2 - 5

Proving LinesParallel

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Lesson 2-5: Proving Lines Parallel 2

Proving Lines Parallel - Postulates & Theorems

If two lines are cut by a transversal and corresponding

angles are congruent, then the lines are parallel.

DC

BA

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Lesson 2-5: Proving Lines Parallel 4

Proving Lines Parallel - Postulates &Theorems

If two lines are cut by a transversal and consecutive

interior angles are supplementary, then the lines are

 parallel.

DC

BA

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Lesson 2-5: Proving Lines Parallel 5

Proving Lines Parallel - Postulates &Theorems

If two lines are cut by a transversal and consecutive

exterior angles are supplementary, then the lines are

 parallel.

DC

BA

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Lesson 2-5: Proving Lines Parallel 6

xamples! Proving Lines Parallel

Find the value of x which will make lines a and lines b parallel.

4. 20Ans"ers! #$ 20 2. !0 ". #0

2$

80 

2x 

b

a#$

60 

3x 

b

a

%$

70 

(x-20) 

b

a $

60 

3x 

b

a

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Lesson 2-5: Proving Lines Parallel 7

'ays to Prove T"o Lines Parallel

$how that corresponding angles are e%ual.

$how that alternative interior angles are e%ual.

$how that consecutive interior angles aresupplementary.

$how that consecutive exterior angles are

supplementary. In a plane, show that the lines are perpendicular to the

same line.