Problem:
In trapezoid ABCD, sides AB and CD are parallel, and diagonal BD and side AD have equal length. If ∠DCB=110∘ and ∠CBD=30∘, then ∠ADB=
Answer Choices:
A. 80∘
B. 90∘
C. 100∘
D. 110∘
E. 120∘
Solution:
In △BDC,∠BDC=40∘. Since DC is parallel to AB,△DBA=40∘. Also, ∠BAD=40∘ since base angles of an isosceles triangle are equal. Therefore ∠ADB=100∘.
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