JEE Main & Advanced Mathematics Three Dimensional Geometry Question Bank Line and Plane

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    The equation of plane through the line of intersection of planes \[ax+by+cz+d=0\], \[a'x+b'y+c'z+d'=0\] and parallel to the line \[y=0,z=0\] is [Kurukshetra CEE 1998]

    A)            \[(ab'-a'b)x+(bc'-b'c)y+(ad'-a'd)=0\]

    B)            \[(ab'-a'b)x+(bc'-b'c)y+(ad'-a'd)z=0\]

    C)            \[(ab'-a'b)y+(ac'-a'c)z+(ad'-a'd)=0\]

    D)            None of these

    Correct Answer: C

    Solution :

                       The equation of a plane through the line of intersection of the planes \[ax+by+cz+d=0\]                    and \[{a}'x+{b}'y+{c}'z+{d}'=0\] is                    \[(ax+by+cz+d)+\lambda ({a}'x+{b}'y+{c}'z+{d}')=0\]            or\[x\,(a+\lambda {a}')+y\,(b+\lambda {b}')+z\,(c+\lambda {c}')+d+\lambda {d}'=0\]?.(i)            This is parallel to x-axis i.e., \[y=0,\,\,z=0\]            \[\therefore \,\,1\,(a+\lambda {a}')+0\,(b+\lambda {b}')+0\,(c+\lambda {c}')=0\,\Rightarrow \,\lambda =-\frac{a}{{{a}'}}\]            Putting the value of l in (i), the required plane is            \[y\,({a}'b-a{b}')+z\,({a}'c-a{c}')+{a}'d-a{d}'=0\]                     i.e., \[\,(a{{b}^{'}}-{{a}^{'}}b)y+\,(a{c}'-{a}'c)z+a{d}'-{a}'d=0\].


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