JEE Main & Advanced Sample Paper JEE Main Sample Paper-39

  • question_answer
    The equation of a circle with origin as centre and passing through the vertices of an equilateral triangle whose median is of length 3a is

    A)  \[{{x}^{2}}+{{y}^{2}}=9{{a}^{2}}\]          

    B)  \[{{x}^{2}}+{{y}^{2}}=16{{a}^{2}}\]

    C)   \[{{x}^{2}}+{{y}^{2}}=4{{a}^{2}}\]         

    D)  \[{{x}^{2}}+{{y}^{2}}={{a}^{2}}\]

    Correct Answer: C

    Solution :

     We know that centroid divides the median in the ratio 2:1. Radius of the circle \[=\frac{2}{3}\times \]length of median \[=\frac{2}{3}\times 3a=2a\]Centre of the (given) circle is C(0, 0). Therefore the equation of the circle \[{{(x-0)}^{2}}+{{(y-0)}^{2}}={{(2a)}^{2}}\Rightarrow {{x}^{2}}+{{y}^{2}}=4{{a}^{2}}\]


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