# Exterior Angles

Author:
MrCarmack
Topic:
Angles
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On the graph below, the arrows pointed to the right mean that the two lines are parallel. Measure ONLY the Exterior Angles: (). Then color the congruent angles the same color.

Which lines above are parallel and how do you know?

These are examples of "Alternate Exterior Angles" and "Same Side Exterior Angles". "Alternate Exterior" means they are on opposite sides of the transversal line (one on the left and one on the right). AND they our OUTSIDE the parallel lines (one on top and one below). "Same Side Exterior" means they are on the same side of the transversal line (both on the right or both on the left). AND they our OUTSIDE the parallel lines (one on top and one below).

and are SAME SIDE EXTERIOR angles because they are both on the right of the transversal and outside the parallel lines (one is on top and one is on the bottom). What is the other pair of Same Side Exterior Angles in the graph above?

and are ALTERNATE EXTERIOR angles because they are on opposite sides of the transveral (one on the right and one on the left) and outside the parallel lines (one is on top and one is on the bottom). What is the other pair of Alternate Exterior Angles in the graph above?

Which definition best describes Alternate Exterior Angles?

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Looking at your graph above, finish this conjecture: "If a transversal crosses two parallel lines, then Alternate Exterior Angles are always..."

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Which definition best describes Same Side Exterior Angles?

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Add up the measure of the Same Side Exterior Angles. What do you notice?

Finish this conjecture: "If a transversal crosses two parallel lines, then Same Side Exterior Angles are always..."

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## Assume Line BD and Line EG are parallel.

Which pair of angles listed below are Alternate Exterior?

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Which pair of angles listed below are Same Side Exterior?

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## Assume Lines BD and EG are parallel.

In the diagram above, if Angle 8 is 120 degrees, then what is the measure of Angle 2?