8th Class Mathematics Exponents and Power Question Bank Exponents and Powers

  • question_answer
    If \[{{27}^{x+1}}={{9}^{x+3}}={{3}^{y}},\] find the respective values of ?x' and 'y'.

    A)  3 and 12     

    B)  12 and 3

    C)  6 and 6      

    D)  4 and 9

    Correct Answer: A

    Solution :

    \[{{27}^{x+1}}={{9}^{x+3}}\] \[\Rightarrow \]               \[{{({{3}^{3}})}^{x+1}}={{({{3}^{2}})}^{x+3}}\] \[\Rightarrow \]               \[{{3}^{3x+3}}={{3}^{2x}}+6\] \[\Rightarrow \]               \[3x+3=2x+6\] \[\Rightarrow \]               \[3x-2x=6-3\]   \[\Rightarrow \]  \[x=3\] Consider   \[{{9}^{x+3}}={{3}^{y}}\]  \[\Rightarrow \]  \[{{({{3}^{2}})}^{x+3}}={{3}^{y}}\] \[\Rightarrow \]               \[{{3}^{2x+6}}={{3}^{y}}\] \[\Rightarrow \]               \[2x+6=y\] \[\therefore \]  \[2(3)+6=y\] \[\Rightarrow \]               \[y=12\]


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