Questions in circle

Select	Question
	The co-ordinates of pole of line $lx+my+n=0$ with respect to circles ${{x}^{2}}+{{y}^{2}}=1$ , is
	The length of common chord of the circles ${{x}^{2}}+{{y}^{2}}=12$ and ${{x}^{2}}+{{y}^{2}}-4x+3y-2=0$ , is
	The length of the common chord of the circles ${{(x-a)}^{2}}+{{(y-b)}^{2}}={{c}^{2}}$ and ${{(x-b)}^{2}}+{{(y-a)}^{2}}={{c}^{2}}$ , is
	The locus of the middle points of chords of the circle ${{x}^{2}}+{{y}^{2}}-2x-6y-10=0$ which passes through the origin, is
	The distance between the chords of contact of the tangents to the circle ${{x}^{2}}+{{y}^{2}}+2gx+2fy+c=0$ from the origin and the point $(g,f)$ is
	The pole of the straight line $x+2y=1$ with respect to the circle ${{x}^{2}}+{{y}^{2}}=5$ is
	A line $lx+my+n=0$ meets the circle ${{x}^{2}}+{{y}^{2}}={{a}^{2}}$ at the points P and Q. The tangents drawn at the points P and Q meet at R, then the coordinates of R is
	Polar of origin (0, 0) with respect to the circle ${{x}^{2}}+{{y}^{2}}+2\lambda x+2\mu y+c=0$ touches the circle ${{x}^{2}}+{{y}^{2}}={{r}^{2}}$ , if
	Tangents AB and AC are drawn from the point $A(0,\,1)$ to the circle ${{x}^{2}}+{{y}^{2}}-2x+4y+1=0$ . Equation of the circle through A, B and C is
	Length of the common chord of the circles ${{x}^{2}}+{{y}^{2}}+5x+7y+9=0$ and ${{x}^{2}}+{{y}^{2}}+7x+5y+9=0$ is