CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2000

  • question_answer
    The direction cosines of a straight line, whose projections on the co-ordinate axes, OX, OY, OZ 12,4,13 respectively, are:

    A)  \[\frac{12}{29},\frac{4}{29},\frac{13}{29}\]

    B)  \[\frac{12}{139},\frac{4}{\sqrt{329}},\frac{13}{\sqrt{329}}\]

    C)  \[\frac{1}{12},\frac{1}{4},\frac{1}{13}\]

    D)  \[\frac{12}{329},\frac{4}{329},\frac{13}{329}\]

    E)  \[\frac{12}{13},\frac{4}{13},1\]

    Correct Answer: B

    Solution :

    Let AB be the given line and the DCs of AB are\[l,m,n.\] Then,                    \[AB.l=12\] \[AB.m=4\] \[AB.n=13\] On squaring and adding both sides, we get \[A{{B}^{2}}({{l}^{2}}+{{m}^{2}}+{{n}^{2}})=144+16+169=329\] \[AB=\sqrt{329}\] \[\therefore \]DCs of AB are\[12/\sqrt{329},4/\sqrt{329},12/\sqrt{329}\]


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