10th Class Mathematics Introduction to Trigonometry Question Bank MCQs - Introduction to Trigonometry

  • question_answer
    If \[\sin \theta \]and \[\cos \theta \] are the roots of the equation \[a{{x}^{2}}-bx+c=0,\] then \[a,b,c\] satisfy the relation:

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

    B) \[{{a}^{2}}-{{b}^{2}}=2ac\]

    C) \[{{a}^{2}}+{{b}^{2}}={{c}^{2}}\]

    D) \[{{a}^{2}}+{{b}^{2}}=2ac\]

    Correct Answer: A

    Solution :

    [a] \[\sin \theta \] and \[\cos \theta \] are the roots,
    \[\sin \theta +\cos \theta =-\left( \frac{-b}{a} \right)\]
    and  \[\sin .\cos =\frac{c}{a}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,{{(\sin \theta +\cos \theta )}^{2}}={{\left( \frac{b}{a} \right)}^{2}}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,{{\sin }^{2}}\theta +{{\cos }^{2}}\theta +2\sin \theta \cdot \cos \theta =\frac{{{b}^{2}}}{{{a}^{2}}}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,1+2\frac{c}{a}=\frac{{{b}^{2}}}{{{a}^{2}}}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,{{a}^{2}}+2ac={{b}^{2}}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,{{b}^{2}}-{{a}^{2}}=2ac\]


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