VIT Engineering VIT Engineering Solved Paper-2010

  • question_answer
    The line joining (5, 0) to \[(10\,\cos \theta ,\,10\sin \theta )\] is divided internally in the ratio 2 : 3 at P. If \[\theta \]varies, then the locus of P is

    A)  a straight line

    B)  a pair of straight lines

    C)  a circle

    D)  None of the above

    Correct Answer: C

    Solution :

    Let coordinate of P are (h, k) then \[h=\frac{2(10cos\theta )+3(5)}{2+3}=4\cos \theta +3\] and \[k=\frac{2\,(10\sin \theta )+3\,(0)}{2+3}=4\sin \theta \] \[\left[ \begin{align}   & \text{Using}\,\text{the}\,\text{internal}\,\text{section}\,\text{formula,} \\  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\begin{matrix}    h=\frac{{{m}_{1}}{{x}_{2}}+{{m}_{2}}{{x}_{1}}}{{{m}_{1}}+{{m}_{2}}}  \\    k=\frac{{{m}_{1}}{{y}_{2}}+{{m}_{2}}{{y}_{1}}}{{{m}_{1}}+{{m}_{2}}}  \\ \end{matrix} \\ \end{align} \right]\] \[\Rightarrow \] \[\frac{h-3}{4}=\cos \theta \]and \[\frac{k}{4}=\sin \theta \] Squaring and adding both of these equations \[\frac{{{(h-3)}^{2}}}{16}+\frac{{{k}^{2}}}{16}={{\cos }^{2}}\theta +{{\sin }^{2}}\theta \] \[\Rightarrow \] \[{{(h-3)}^{3}}+{{k}^{2}}=16\] Therefore, locus of point P is \[{{\left( x-3 \right)}^{2}}+{{y}^{2}}=16\] which is a circle.


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