In the given figure, CDEF is a cyclic quadrilateral, DEandCF are produced to AandB respectively such that AB∥CD. If ∠FED=80∘, find ∠FBA.
A
30∘
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B
60∘
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C
80∘
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D
10∘
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Solution
The correct option is C80∘ CDEFisacyclicquadrilateral.∠FED=80o(Given)∠FED+∠FCD=180o...(sumofoppositeanglesofcyclicquadrilateralis180o)⇒FCD=180o−80o=100o.SinceAB∥CD,⇒ABCDisaparallelogram.∠ABC+∠BCD=180o...(Adjacentanglesofparallelogram.aresupplementary)∠BCD=∠FCD=100o⇒∠ABC=180o−100o=80o∠ABC=∠FBA=80o.Hence,optionCiscorrect.