9th Class Mathematics Circles Question Bank Circles

  • question_answer
    In the given figure, AB and BC are two chords of the circle with centre O, where\[\angle BAO={{50}^{o}};\]\[\angle BCO={{35}^{o}},\] then \[\angle AOC\]is equal to ____.  

    A) \[{{170}^{o}}\]

    B)        \[{{70}^{o}}\]                        

    C)        \[{{150}^{o}}\]                                  

    D)         None of these

    Correct Answer: A

    Solution :

    Given, \[\angle BAO={{50}^{o}},\angle BCO={{35}^{o}}\]     ?(i) Now, OA = OB              (radii of circle) \[\Rightarrow \]\[\angle BAO=\angle OBA\] (Angles opposite to equal sides are equal) \[\Rightarrow \]\[\angle OBA={{50}^{o}}\]                                 [From (i)] Similarly, \[OB=OC\Rightarrow \angle BCO=\angle OBC\] \[\Rightarrow \] \[\angle OBC={{35}^{o}}\]                    [From (i)] Now, \[\angle ABC=\angle OBA+\angle OBC={{50}^{o}}+{{35}^{o}}={{85}^{o}}\] \[\therefore \]\[\angle AOC=2\angle ABC=2({{85}^{o}})={{170}^{o}}\]


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