Elementary Mathematics
Lesson 113
Lines and Angles
Turning lines
Angles
A ray turns from 45° (acute) to 90° (right) to 135° (obtuse).
Angles
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Conceptual model: a simplified teaching picture.
Use the corner of a book to check corners in the room. Turn two pencils joined at one end.A door corner is …
An angle measures the amount of turn between two lines.