# 3.1 Identify Pairs of Lines and Angles

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3.1 Identify Pairs of Lines and Angles

Parallel Lines Coplanar Do not intersect
Triangles, like those above in red, indicate that 2 lines are parallel. D B Coplanar Do not intersect Segments and rays are parallel if they lie on parallel lines. C

Parallel planes if they never intersect

B C D A F G E H

B C A D F G E H

Skew Lines: Do not intersect, but do not lie in the same plane.
G C B

A D E H G C B F

B C D A F G E H

#13: Parallel Postulate If there is a line and a point not on the line,

#13: Parallel Postulate If there is a line and a point not on the line, then there is exactly one line through the point and parallel to the line

#14: Perpendicular Postulate
If there is a line and a point not on the line, then there is exactly one line through the point and perpendicular to the line

Corresponding Angles Same side of transversal Corresponding position
Transversal; intersects 2 or more coplanar lines Corresponding Angles Same side of transversal Corresponding position

Alternate Exterior Angles “Alternate”  opposite sides of transversal “Exterior”  outside of the two lines

Alternate Interior Angles “Alternate”  opposite sides of transversal “Interior”  inside of the two lines

Consecutive Interior Angles “Consecutive”  “together”; same side of the transversal “Interior”  inside of the two lines

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