Questions in circle

Select	Question
	The radius of the circle ${{x}^{2}}+{{y}^{2}}+4x+6y+13=0$ is
	Let $P({{x}_{1}},{{y}_{1}})$ and $Q({{x}_{2}},{{y}_{2}})$ are two points such that their abscissa ${{x}_{1}}$ and ${{x}_{2}}$ are the roots of the equation ${{x}^{2}}+2x-3=0$ while the ordinates ${{y}_{1}}$ and ${{y}_{2}}$ are the roots of the equation ${{y}^{2}}+4y-12=0$ . The centre of the circle with PQ as diameter is
	Four distinct points $(2k,\,3k),(1,0)(0,1)$ and $(0,0)$ lie on a circle for
	If one end of the diameter is (1, 1) and other end lies on the line $x+y=3$ , then locus of centre of circle is
	A circle is drawn to cut a chord of length 2a units along X-axis and to touch the Y-axis. The locus of the centre of the circle is
	If the length of tangent drawn from the point (5, 3) to the circle ${{x}^{2}}+{{y}^{2}}+2x+ky+17=0$ be 7, then $k =$
	The line $lx+my+n=0$ will be a tangent to the circle ${{x}^{2}}+{{y}^{2}}={{a}^{2}}$ iff
	The angle between the two tangents from the origin to the circle ${{(x-7)}^{2}}+{{(y+1)}^{2}}=25$ is
	A pair of tangents are drawn from the origin to the circle ${{x}^{2}}+{{y}^{2}}+20(x+y)+20=0$ . The equation of the pair of tangents is
	If OA and OB be the tangents to the circle ${{x}^{2}}+{{y}^{2}}-6x-8y+21=0$ drawn from the origin O, then $AB =$