Santiago notices that when a pair of parallel lines is cut by a transversal and one angle is a right angle (90 degrees) all of the othe angles are also right angles. use words, numbers, and drawings to explain why santiago's observation is true.

If the lines are parallel, then they are equidistant from each other and will always be like that no matter what, they will never cross. a line also equals 180 degrees.
if the transversal create one 90 degree angle, then its supplementary angle also has to be 90 degrees. then using alternate interior angles you would know the other two angles on the other line.

hope this helped