9th Class Mathematics Lines and Angles Question Bank Lines and Angles

  • question_answer
    In the given figure, if OCD is an isosceles triangle in which OD and OC are equal, then what will be the value of \[\angle OCD?\]

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

    B)        \[{{50}^{o}}\]

    C)        \[{{65}^{o}}\]

    D)        \[{{45}^{o}}\]

    Correct Answer: C

    Solution :

    \[x+{{10}^{o}}+x+x+{{20}^{o}}={{180}^{o}}\] \[\Rightarrow \]\[3x+{{30}^{o}}={{180}^{o}}\Rightarrow 3x={{150}^{o}}\] \[\Rightarrow \]\[x={{50}^{o}}\] \[\angle OCD=\angle ODC\]         \[[\because \,OD=OC]\] Now, \[\angle C+\angle D+x={{180}^{o}}\] \[\Rightarrow \]\[\angle OCD+\angle OCD+{{50}^{o}}={{180}^{o}}\] \[\Rightarrow \]\[2\angle OCD={{130}^{o}}\Rightarrow \angle OCD=\angle {{65}^{o}}\]


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