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Mathematics 21 Online
OpenStudy (anonymous):

Can anybody help me with this?

OpenStudy (mathstudent55):

What?

OpenStudy (anonymous):

OpenStudy (mathstudent55):

You can start with the given.

OpenStudy (mathstudent55):

How do you prove two lines are parallel?

OpenStudy (anonymous):

<5 congruent to <6 and <6 congruent to <4

OpenStudy (anonymous):

Can you help me continue? @mathstudent55

OpenStudy (mathstudent55):

You can write those two statements. The reasons are "Given."

OpenStudy (mathstudent55):

|dw:1372954322542:dw|

OpenStudy (anonymous):

I did that. thanks. what could I do next?

OpenStudy (mathstudent55):

If lines m and n are parallel, then angles 1 and 2 are congruent. If angles 1 and 2 are congruent, then lines m and n are parallel. You need the second postulate to prove lines parallel.

OpenStudy (mathstudent55):

Since angle 5 is congruent to angle 6, and angle 6 is congruent to angle 4, can you conclude anything about angle 5 and angle 4?

OpenStudy (anonymous):

they are also congruent?

OpenStudy (mathstudent55):

Right.

OpenStudy (mathstudent55):

That is your next statement. <5 is congruent to <4 The reason is "transitive property of congruence"

OpenStudy (anonymous):

thank you so much!!!

OpenStudy (mathstudent55):

|dw:1372954752372:dw|

OpenStudy (mathstudent55):

Now look at the figure above. If angle 1 is congruent to abngle 2, then lines m and n are parallel. Angles 1 and 2 are called alternate interior angles. A theorem states: If two lines are cut by a transversal such that alternate interior angles are congruent, then the lines are parallel.

OpenStudy (anonymous):

Sorry in the first sentence you wrote angle 5 and 5?

OpenStudy (mathstudent55):

In your case, angles 4 and 5 are congruent. Angles 4 anf 5 are alternate interior angles, so lines AD and BC are parallel. Your last statement is line AD is parallel to line BC Reason: If two lines are cut by a transversal such that alternate interior angles are congruent, then the lines are parallel.

OpenStudy (mathstudent55):

I fixed it.

OpenStudy (anonymous):

Thank you so much!!!!!!!!!!!

OpenStudy (mathstudent55):

wlcm

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