A straight angle measures exactly 180 degrees.
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Perpendicular lines intersect at right angles. The symbol ⊥ is used to indicate that two lines are perpendicular.
The edge is the line segment where two faces of a solid figure intersect.
An angle is formed by two rays that share a common endpoint called the vertex. Angles are found wherever lines or line segments intersect.
Use symbolic notation to describe parallel lines and perpendicular lines. (b)