CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    If\[\sec \theta \]and\[\tan \theta \]are the roots of \[a{{x}^{2}}+bx+c=0;\]\[(a,b\ne 0)\]then the value of\[\sec \theta -\tan \theta \]is

    A)  \[-\frac{a}{b}\]                                

    B)  \[\frac{\sqrt{{{b}^{2}}-4ac}}{a}\]

    C)  \[1-\frac{a}{b}\]             

    D)         \[1+\frac{{{a}^{2}}}{{{b}^{2}}}\]

    E)  \[\frac{a}{b}\]

    Correct Answer: B

    Solution :

    Since,\[sec\theta \]and\[\tan \theta \]are the roots of the equation\[a{{x}^{2}}+bx+c=0\]. Then, \[\sec \theta +\tan \theta =-\frac{b}{a}\] and \[\sec \theta .\tan \theta =\frac{c}{a}\] Now, \[{{(\sec \theta -\tan \theta )}^{2}}\] \[={{(\sec \theta +\tan \theta )}^{2}}-4\sec \theta .\tan \theta \] \[={{\left( -\frac{b}{a} \right)}^{2}}-4\left( \frac{c}{a} \right)\] \[=\frac{{{b}^{2}}}{{{a}^{2}}}-\frac{4c}{a}\] \[\Rightarrow \] \[(\sec \theta -\tan \theta )=\frac{\sqrt{{{b}^{2}}-4ac}}{a}\]


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