Answer:
If the two lines intersect at a point, the vertical angles formed are congruent. The intersecting lines either form a pair of acute angles and a pair of obtuse angles, or the intersecting lines form four right angles. When the lines meet to form four right angles, the lines are perpendicular.
The main fact to establish about perpendicular lines has to do with uniqueness. Remember that that the midpoint of a line segment and the angle bisector of an angle are unique. You learned that if you are given a point and a line, there is a unique line passing through that point that is perpendicular to the line. You now have the skills to establish the uniqueness property of perpendicular lines.
Step-by-step explanation:
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