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7th Class Mathematics Integers Question Bank Number System

  • question_answer
    If \[{{2}^{x-1}}+{{2}^{x+1}}=\mathbf{640,}\] the value of x is

    A)  7                    

    B)  8  

    C)  9                                

    D)  6

    Correct Answer: B

    Solution :

    (b): \[{{2}^{X-}}^{1}+{{2}^{X+1}}=640\] \[={{2}^{x-1}}+4\times {{2}^{x-1}}=640\] Put, \[{{2}^{x-1}}=P\] \[\Rightarrow 5P=640\Rightarrow P=128\] \[{{2}^{x-1}}=128\Rightarrow x-1=7\] \[\Rightarrow x=8.\]


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