9th Class Mathematics Circles Question Bank Circles

  • question_answer
    BC is a chord of a circle with centre O. A is a point on major arc BC. Find the total measure of \[\angle BAC\]and \[\angle OBC\]

    A) \[90{}^\circ \]                            

    B) \[100{}^\circ \]

    C) \[120{}^\circ \]

    D) \[150{}^\circ \]

    Correct Answer: A

    Solution :

    Refer the question figure. In \[\Delta OBC,OB=OC\](= radius) \[\Rightarrow \]\[\angle OBC=\angle OCB=y\] Now, \[z+y+y={{180}^{o}}\] \[\Rightarrow \] \[z={{180}^{o}}-2y\]                     ?..(i) Also, \[\angle BOC=2\angle BAC\] \[\Rightarrow \]\[z=2x\]                                   ?...(ii) From (i) and (ii),          \[\Rightarrow \]\[2x+2y={{180}^{o}}\Rightarrow x+y={{90}^{o}}\] \[\therefore \]\[\angle BAC+\angle OBC={{90}^{o}}\]


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