BCECE Engineering BCECE Engineering Solved Paper-2009

  • question_answer
    If \[\sin \alpha ,\cos \alpha \]are the roots of the equation\[a{{x}^{2}}+bx+c=0,(c\ne 0),\]the

    A) \[{{a}^{2}}-{{b}^{2}}+2ac=0\]

    B)  \[{{(a+c)}^{2}}={{b}^{2}}-{{c}^{2}}\]

    C)  \[{{a}^{2}}+{{b}^{2}}-2ac=0\]

    D)  \[{{(a-c)}^{2}}={{b}^{2}}+{{c}^{2}}\]

    Correct Answer: A

    Solution :

    Given equation is \[a{{x}^{2}}+bx+c=0\] \[\therefore \]  \[\sin \alpha +\cos \alpha =-\frac{b}{a}\] and        \[\sin \alpha \cos \alpha =\frac{c}{a}\] \[\Rightarrow \]\[{{\sin }^{2}}\alpha +{{\cos }^{2}}\alpha +2\sin \alpha \cos \alpha =\frac{{{b}^{2}}}{{{a}^{2}}}\] and \[\sin \alpha \cos \alpha =\frac{c}{a}\] \[\Rightarrow \]\[1+\frac{2c}{a}=\frac{{{b}^{2}}}{{{a}^{2}}}\] \[\Rightarrow \]\[{{a}^{2}}+2ac={{b}^{2}}\] \[\Rightarrow \] \[{{a}^{2}}-{{b}^{2}}+2ac=0\]


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