7th Class Mathematics Lines and Angles Question Bank Lines And Angles

  • question_answer
    In the figure (not drawn to scale), AB is parallel to CD and \[\angle ECD\]is a right angle. Find \[\angle y\].                        

    A)  \[{{111}^{o}}\]                  

    B)  \[{{112}^{o}}\]      

    C)  \[{{113}^{o}}\]      

    D)         \[{{114}^{o}}\]                  

    Correct Answer: B

    Solution :

    Since, \[AB||CD\] \[\therefore \] \[\angle CAB+\angle DCA={{180}^{o}}\] (Co-interior angles) \[\therefore \]  \[{{22}^{o}}+\angle DCA={{180}^{o}}\] \[\Rightarrow \] \[\angle DCA={{180}^{o}}-{{22}^{o}}={{158}^{o}}\] Also, \[\angle ECD+\angle DCA+\angle y={{360}^{o}}\] (Angles about a point)             \[\Rightarrow \] \[{{90}^{o}}+{{158}^{o}}+\angle y={{360}^{o}}\] \[\Rightarrow \]\[\angle y={{360}^{o}}-({{90}^{o}}+{{158}^{o}})\] \[\Rightarrow \] \[\angle y={{360}^{o}}-{{248}^{o}}={{112}^{o}}\]


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