JEE Main & Advanced Mathematics Rectangular Cartesian Coordinates Question Bank Points related to triangle (Orthocente Circumcentre Incentre), Area of some geometrical figures Collinearity

  • question_answer
    If the points \[(a,\,0),\ (0,\,b)\]and (1, 1) are collinear, then   

    A) \[\frac{1}{{{a}^{2}}}+\frac{1}{{{b}^{2}}}=1\]

    B) \[\frac{1}{{{a}^{2}}}-\frac{1}{{{b}^{2}}}=1\]

    C) \[\frac{1}{a}+\frac{1}{b}=1\]

    D) \[\frac{1}{a}-\frac{1}{b}=1\]

    Correct Answer: C

    Solution :

    \[\frac{1}{2}\,\left| \,\begin{matrix}    a & 0 & 1  \\    0 & b & 1  \\    1 & 1 & 1  \\ \end{matrix}\, \right|=0\,\,\Rightarrow \,\,a\,(b-1)+0+1\,(-b)=0\] \[\Rightarrow \,\,ab-a-b=0\,\,\,\Rightarrow \,\,\frac{1}{a}+\frac{1}{b}=1\].


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