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

  • question_answer
    If \[RS||PQ\]and \[RT||UQ,\] then find the value of\[8x-2y\].                     

    A)  \[{{60}^{o}}\]                                

    B)  \[{{30}^{o}}\]        

    C)         \[{{150}^{o}}\]      

    D)         \[{{100}^{o}}\]

    Correct Answer: A

    Solution :

    Since, \[RT||UQ\]and QR is a transversal. \[\angle UQR=\angle QRT\] (Alternate angles) \[\Rightarrow \] \[y={{90}^{o}}\] Also, \[\angle PQU+{{150}^{o}}={{180}^{o}}\](Linear pair) \[\Rightarrow \]  \[\angle PQU={{180}^{o}}-{{150}^{o}}={{30}^{o}}\] And \[PQ||RS\]and RQ is transversal. \[\angle PQR=\angle QRS~~\] (Alternate angles) \[\Rightarrow \]  \[\angle PQU+\angle UQR=\angle SRT+\angle TRQ\] \[\Rightarrow \] \[{{30}^{o}}+{{90}^{o}}=x+{{90}^{o}}\Rightarrow x={{30}^{o}}\] Now, \[8x-2y\text{ =}8\times {{30}^{o}}-2\times {{90}^{o}}\] \[={{240}^{o}}-{{180}^{o}}={{60}^{o}}\]


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