10th Class Mathematics Coordinate Geometry Question Bank Coordinate Geometry

  • question_answer
    Four vertices of a parallelogram taken in order are \[(-3,-1),\,(a,b),\,(3,3)\]and\[(4,3)\]. What will be the ratio of a and b?

    A)  \[4:1\]                         

    B)  \[1:2\] 

    C)         \[1:3\]                         

    D)  \[3:1\] 

    Correct Answer: A

    Solution :

    Let points be \[A(-3,-1),B(a,b),\,C(3,3)\] and \[D(4,3)\]. So, coordinates of the mid-point of AC = coordinates of the mid-point of BD [\[\because \] In parallelogram, diagonals bisect each other] \[\Rightarrow \]            \[\left( \frac{-3+3}{2},\frac{-1+3}{2} \right)=\left( \frac{a+4}{2},\frac{b+3}{2} \right)\] \[\Rightarrow \]            \[(0,1)=\left( \frac{a+4}{2},\frac{b+3}{2} \right)\] \[\Rightarrow \]            \[\frac{a+4}{2}=0\] and \[\frac{b+3}{2}=1\] \[\Rightarrow \]            \[a=-4\] and \[b=-1\] Now, \[\frac{a}{b}=\frac{-4}{-1}=\frac{4}{1}\Rightarrow a:b=4:1\]


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