7th Class Mathematics The Triangle and its Properties Question Bank Triangles

  • question_answer
    In the figure given, what are the values of \[\angle b,\,\,\angle c\] and \[\angle a\] respectively?                                

    A)                  \[{{18}^{o}},{{70}^{o}}\] and \[{{92}^{o}}\]

    B)                  \[{{92}^{o}},\,{{70}^{o}}\] and \[{{18}^{o}}\]

    C)                  \[{{70}^{o}},{{92}^{o}}\] and \[{{18}^{o}}\]  

    D)                  \[{{70}^{o}},{{18}^{o}}\] and \[{{92}^{o}}\]

    Correct Answer: C

    Solution :

       Given \[AB=BD\] \[\Rightarrow \]               \[\angle BAD=\angle BAD={{35}^{o}}\]                 \[\angle b=\angle BDA+\angle BAD\] \[\Rightarrow \]               \[\angle b={{35}^{o}}+{{35}^{o}}={{70}^{o}}\] Also given \[AC=CE\]                 \[\Rightarrow \]               \[\angle CAE=\angle CEA={{46}^{o}}\] Using exterior angle property, \[\Rightarrow \]               \[\angle c=\angle CAE+\angle CEA\]                 \[={{46}^{o}}+{{46}^{o}}={{92}^{o}}\] In  \[\Delta ABC,\] \[\angle a+\angle b+\angle c={{180}^{o}}\] \[\Rightarrow \]               \[\angle a={{180}^{o}}-\angle b-\angle c\] \[\Rightarrow \]               \[\angle a={{180}^{o}}-{{70}^{o}}-{{92}^{o}}={{18}^{o}}\] \[\therefore \]  \[\angle a={{18}^{o}},\angle b={{70}^{o}}\] and \[\angle c={{92}^{o}}\]


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