Angles #ABC# and #DBE# are vertical angles. If the measure of #/_ABC# is 40°, what is the measure of #/_ ABD#?

1 Answer
Alan P.
Feb 2, 2016

Either #180^@# or #140^@#

Explanation:

Definition:
vertical angles: the angles opposite each other when two lines intersect.

Case 1
If the ends of the angles have been specified in a consistent order (e.g. counter clockwise)
#/_ABD# forms a straight line.

Case 2
If the ends of the angles have been specified in opposite orders)
#/_ABD# is the complement of #/_ABC#

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