JEE Main & Advanced Mathematics Circle and System of Circles Question Bank Tangent and normal to a circle

  • question_answer
    Square of the length of the tangent drawn from the point \[(\alpha ,\beta )\]to the circle \[a{{x}^{2}}+a{{y}^{2}}={{r}^{2}}\]is

    A)            \[a{{\alpha }^{2}}+a{{\beta }^{2}}-{{r}^{2}}\]           

    B)            \[{{\alpha }^{2}}+{{\beta }^{2}}-\frac{{{r}^{2}}}{a}\]

    C)            \[{{\alpha }^{2}}+{{\beta }^{2}}+\frac{{{r}^{2}}}{a}\]          

    D)            \[{{\alpha }^{2}}+{{\beta }^{2}}-{{r}^{2}}\]

    Correct Answer: B

    Solution :

               Length of tangent is\[\sqrt{{{S}_{1}}}\].                    Equation of circle is \[{{x}^{2}}+{{y}^{2}}-\frac{{{r}^{2}}}{a}=0\]                    Hence\[{{S}_{1}}={{\alpha }^{2}}+{{\beta }^{2}}-\frac{{{r}^{2}}}{a}\].


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