8th Class Mathematics Algebraic Expressions Question Bank Algebra

  • question_answer
    If the difference of the squares of two numbers is 45, the square of the smaller number is 4 times the larger number, then the numbers are

    A) 9,6 or 9,-6       

    B) 5,6 or 5,-6

    C) 9,5 or 9,-5                   

    D) None of these

    Correct Answer: A

    Solution :

    Let the two numbers are a and b such that a > b. By hypothesis,                         \[{{a}^{2}}-{{b}^{2}}=45\]                    ?(1) And      \[11x+12y=58\]                      ...(2) Substituting the value of \[12x+11y=57,\] from equation (2) in equation (i), we have \[4(x+y)\] or \[{{a}^{2}}-4a-45=0\]  or \[{{a}^{2}}-9a+5a-45=0\] or \[a\,(a-9)+5\,(a-9)=0\]or \[(a-9)\,(a+5)=0\] or \[a=9,\,\,-5\] Substituting these values for a separately in equation (2), we have \[{{x}^{2}}-x-6=0?\]                                   \[(0,\frac{1}{2})\] \[(-2,3)\]                                   \[(\frac{1}{2},1)\] But \[(2,\frac{1}{2})\]cannot be negative, therefore \[5{{x}^{2}}-7x-6=0\]    \[\left( -\frac{3}{5},2 \right)\]       \[(1,1)\] Hence,             \[a=9,\]                       \[b=\pm 6\]


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