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 Everyday Examples
Alternate Interior Angles:  Alternate interior angles are pairs of angles formed when a third line (a transversal) crosses two other lines. These angles are on opposite sides of the transversal and are in between the other two lines.
 Image source: http://www.polarfocus.com/graphics/elevman.gif Only an angle and measured distance along the ground are needed to determine the height of objects far from the ground. Two possible angles can be measured to help determine this information: the angle of elevation from the ground or the angle of depression from the top of the object. The angle of elevation is the angle from the ground that is aimed towards the top of the of the object. The angle of depression is the angle from the horizontal line of sight at the top of the object directed towards a spot, or an observer, on the ground. Each of these angles has the same measure because they are congruent alternate interior angles that share a transversal that intersects parallel lines (the ground and horizontal view from the top of the building).