JEE Main & Advanced JEE Main Paper (Held On 26 May 2012)

  • question_answer
    The number of common tangents of the circles given by\[{{x}^{2}}+{{y}^{2}}-8x-2y+1=0\]and\[{{x}^{2}}+{{y}^{2}}+6x+8y=0\]is.   JEE Main Online Paper (Held On 26-May-2012)  

    A) one                                       

    B)                        four

    C)                        two    

    D)                        three

    Correct Answer: C

    Solution :

                    Given circles are \[{{x}^{2}}+{{y}^{2}}-8x-2y+1=0\] and\[{{x}^{2}}+{{y}^{2}}+6x+8y=0\] Their centres and radius are \[{{C}_{1}}(4,1){{r}_{1}}=\sqrt{16}=4\] \[{{C}_{2}}(-3,-4),{{r}_{2}}=\sqrt{25}=5\] \[{{r}_{1}}-{{r}_{2}}=-1,{{r}_{1}}+{{r}_{2}}=9\] Since, \[{{r}_{1}}-{{r}_{2}}<{{C}_{1}}{{C}_{2}}<{{r}_{1}}+{{r}_{2}}\] \[\therefore \]Number of common tangents = 2                                


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