JCECE Engineering JCECE Engineering Solved Paper-2013

  • question_answer
    If \[{{x}_{1}}\] and \[{{x}_{2}}\] are two distinct roots of the equation\[a\cos x+b\sin x=c\], then\[\tan \frac{{{x}_{1}}+{{x}_{2}}}{2}\] is equal to

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

    B) \[\frac{b}{a}\]

    C) \[\frac{c}{a}\]                                   

    D) \[\frac{a}{c}\]

    Correct Answer: B

    Solution :

    \[\cos x+b\sin x=c\] \[\Rightarrow \]               \[a\frac{\left( 1-{{\tan }^{2}}\frac{x}{2} \right)}{\left( 1+{{\tan }^{2}}\frac{x}{2} \right)}+\frac{2b\tan \frac{x}{2}}{1+{{\tan }^{2}}\frac{x}{2}}=c\] \[\Rightarrow \]               \[(c+a){{\tan }^{2}}\frac{x}{2}-2b\tan \frac{x}{2}+c-a=0\] \[\Rightarrow \]               \[\tan \frac{{{x}_{1}}}{2}+\tan \frac{{{x}_{2}}}{2}=\frac{2b}{c+a}\]                 \[\tan \frac{{{x}_{1}}}{2}\cdot \tan \frac{{{x}_{2}}}{2}=\frac{c-a}{c+a}\] \[\Rightarrow \]               \[\tan \left( \frac{{{x}_{1}}+{{x}_{2}}}{2} \right)=\frac{\frac{2b}{c+a}}{1-\frac{c-a}{c+a}}\]                                                 \[=\frac{2b}{2a}=\frac{b}{a}\]


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