Co - interior Angles Theorem
In the applet below, a TRANSVERSAL intersects 2 PARALLEL LINES. 
When this happens, there are 2 pairs of SAME-SIDE INTERIOR ANGLES that are formed.  
Interact with the applet below for a few minutes, then answer the questions that immediately follow.
Directions & Questions:  
1) Complete the following statement:  If a transversal intersects 2 ________________    ______________, then co-interior angles are _____________________.  
2) If the gray angle above measures 120 degrees, what would the measure of its co-interior angle be?
3) As you moved the slider, what transformation(s) took place?