BCECE Engineering BCECE Engineering Solved Paper-2008

  • question_answer
    If \[\theta \]is the angle between the curves \[xy=2\]and \[{{x}^{2}}+4y=0,\]then \[\tan \theta \]is equal to

    A)  1                            

    B)  -1          

    C)  2        

    D)  3

    Correct Answer: D

    Solution :

    Given equation of curves are \[xy=2\]                                               ?(i)                 and        \[{{x}^{2}}+4y=0\]                           ?(ii) On solving Eqs. (i) and (ii), we get point of intersection is \[-(2,-1).\] From Eq. (i)                                 \[x\frac{dy}{dx}+y=0\]                 \[\Rightarrow \]               \[\frac{dy}{dx}=-\frac{y}{x}\]                 \[{{m}_{1}}={{\left( \frac{dy}{dx} \right)}_{(-2,-1)}}=-\frac{1}{2}\] and from Eq. (ii), \[2x+4\frac{dy}{dx}=0\]                 \[\Rightarrow \]               \[{{m}_{2}}=1\]                 \[\because \]     \[\tan \theta =\left| \frac{{{m}_{1}}-{{m}_{2}}}{1+{{m}_{1}}{{m}_{2}}} \right|=\left| \frac{-\frac{1}{2}-1}{1-\frac{1}{2}} \right|=\left| \frac{\frac{3}{2}}{\frac{1}{2}} \right|\]                 \[\therefore \]  \[\tan \theta =3\]


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