JEE Main & Advanced Mathematics Straight Line Question Bank Self Evaluation Test - Straight Lines & Pair Striaght Lines

  • question_answer
    Locus of centroid of the triangle whose vertices are \[(\alpha cos\,t,a\,sin\,t),(b\,sin\,t,-b\,cos\,t)\] and \[(1,0)\], where t is a parameter, is

    A) \[{{(3x+1)}^{2}}+{{(3y)}^{2}}={{a}^{2}}-{{b}^{2}}\]

    B) \[{{(3x-1)}^{2}}+{{(3y)}^{2}}={{a}^{2}}-{{b}^{2}}\]

    C) \[{{(3x-1)}^{2}}+{{(3y)}^{2}}={{a}^{2}}+{{b}^{2}}\]

    D) \[{{(3x+1)}^{2}}+{{(3y)}^{2}}={{a}^{2}}+{{b}^{2}}\]

    Correct Answer: C

    Solution :

    [c] \[x=\frac{a\cos t+b\sin t+1}{3}\] \[\Rightarrow a\cos t+b\sin t=3x-1\] \[y=\frac{a\sin t-b\cos t}{3}\Rightarrow a\sin t-b\cos t=3y\] Squaring & adding, \[{{(3x-1)}^{2}}+{{(3y)}^{2}}={{a}^{2}}+{{b}^{2}}\]


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