10th Class Mathematics Related to Competitive Exam Question Bank Algebra

  • question_answer
    If 14 is the maximum of- \[-\lambda {{x}^{2}}+\lambda x+8\], then the value of \[\lambda \] is

    A)  24                           

    B)         \[6\sqrt{3}\]

    C)  \[-6\sqrt{3}\]                   

    D)         - 12

    Correct Answer: A

    Solution :

                    \[y=-\lambda \left[ {{x}^{2}}-x-\frac{8}{\lambda } \right]\]                    \[=-\lambda \left[ {{\left( x-\frac{1}{2} \right)}^{2}}-\frac{1}{4}-\frac{8}{\lambda } \right]\]                    \[=-\lambda {{\left( x-\frac{1}{2} \right)}^{2}}-\frac{\lambda }{4}+8\] \[y\] is maximum when\[x=\frac{1}{2}\] \[i.e.\]  \[\frac{\lambda }{4}+8=14\] or                  \[\lambda =24\]


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