Three students attempt to define what it means for AB and CD to be perpendicular. o
D
B
Can you match the teacher's comments to the definitions?
Definition of perpendicular lines
Teacher's comments
Daniela's definition: AB is perpendicular
Please rework your definition to use more precise
to CD is the measure of ZAOC equals
mathematical language.
the measure of LAOD.
Oris definition: AB is perpendicular to
CD i AB and CD intersect perfectly
sideways.
Well done! I hadn't previously considered defining
perpendicular lines in terms of a rigid transformation like
rotation, but by golly it works!
Kaori's definition: AB is perpendicular to
Dit one line can be mapped to the other
by a rotation about point of 90
Well done! Because the measure of ZCOD is 180° (by
the definition of a straight angle), the measures of angles
ZAOC and ZAOD must both be 90.
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