Browse Questions

The centre of the circle passes through $(0,0)$ and $(1,0)$ and touching the circle $x^2+y^2=9$ is

$\begin{array}{1 1}(A)\;\bigg(\frac{1}{2},\frac{1}{2}\bigg) \\(B)\;\bigg(\frac{1}{2},-\sqrt 2\bigg) \\(C)\;\bigg(\frac{3}{2},\frac{1}{2}\bigg) \\(D)\;\bigg(\frac{1}{2},\frac{3}{2}\bigg) \end{array}$

Let the requirement circle be
$x^2+y^2+2gx+2fy+c=0$
Since it passes through $(0,0)$ and $(1,0)$
=> $C=0$ and $g=\large\frac{-1}{2}$
Points $(0,0)$ and $(1,0)$ lie inside the circle $x^2+y^2=9$ So two circles touch internally
=> $C_1C_2= r_1-r_2$
$\sqrt {g^2+f^2}=3 -\sqrt {g^2+f^2}$
=> $\sqrt {g^2+f^2}=\large\frac{3}{2}$
=> $f^2=\large\frac{9}{4}-\frac{1}{4}$$=2 Hence the centres of required circle are \bigg(\large\frac{1}{2},$$-\sqrt 2\bigg)$
Hence B is the correct answer.