Lesson 5-2  Special       

1.  RECALL  from another lesson that we studied angles created by parallel lines.

     RECALL a Z shape or N shape is created by 2 Alternate Interior angles.  Z  N See the 2  angles in each letter.

     LOOK for them below. If they are congruent then two of the lines (creating those angles) are parallel.

2.  Also recall if 2 lines are PERPENDICULAR to a third line then

     the 2 lines must be parallel to each other.    ^|__|

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Recall the red arrows indicate parallel lines and

      the red sticks indicate congruent (equal) line segments (sides).

	Decide if these are parallelograms and if they are then how do you know? You must know the 4 theorems and the definition of parallelogram.
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Susan O. Johnsey	www.mathinabox.com	Math in a Box 2007

In problem 9 above  do you see the N or Z shape that the alternate interior angles create.   When they are congruent then we know we have parallel lines.   See the two angles with one arc on them.   And see the two angles with the two-arcs on them.  They are congruent alternate interior angles thus we have two pair of parallel lines.