\[Equation\]	\[Graph\]	\[Centre\]	\[Radius\]
\[x^2+y^2=a^2\]		\[(0,0)\]	\[a\]
\[(x-h)^2+(y-k)^2=a^2\]		\[(h,k)\]	\[a\]
\[x^2+y^2+2gx+2fy+c=0\]		\[(-g,-f)\]	\[\sqrt{g^2+f^2-c}\]

Equations of Tangent of all Circles

\[Equations\space of\] \[Circle\]	\[Point/Line\space of\space contact\space of \space \] \[circle \] \[\ m=slope \space of \space tangent\]	\[Equation\space of\space \] \[ tangent\]
\[x^2+y^2=a^2\]	\[(x1,y1)\]	\[xx1 +yy1=a^2\]
\[x^2+y^2=a^2\]	\[(a \space cos\theta,b \space sin\theta)\]	\[x \space cos\theta + y \space sin\theta=a\]
\[x^2+y^2=a^2\]	\[y=mx+c\]	\[y=mx±a\sqrt{1+m^2}\]
\[x^2+y^2+2gx+2fy+c=0\]	\[(x1,y1)\]	\[xx1+yy1+g(x+x1)+f(y+y1)+c=0\]

Equations of Normal of all Circles

\[Equations\space of\] \[Circle\]	\[Point/Line\space of\space contact\space of \space \] \[circle \] \[\ m=slope\space of \space tangent\]	\[Equation\space of\space\] \[\ Normal\]
\[x^2+y^2=a^2\]	\[(x1,y1)\]	\[\frac{x}{x1}=\frac{y}{y1}\]
\[x^2+y^2=a^2\]	\[(a \space cos\theta,b \space sin\theta)\]	\[y=x\space tan\theta\]
\[x^2+y^2=a^2\]	\[y=mx+c\]	\[x+my=±a\sqrt{1+m^2}\]
\[x^2+y^2+2gx+2fy+c=0\]	\[(x1,y1)\]	\[\frac{y-y1}{x-x1}=\frac{y1+f}{x1+g}\]

Director Circle of all Circles

\[Equations\space of\space Circle\]	\[Equation\space of\space Director\space Circle\]
\[x^2+y^2=a^2\]	\[x^2+y^2=2 \space a^2\]
\[(x-h)^2+(y-k)^2=a^2\]	\[(x-h)^2+(y-k)^2=2 \space a^2\]
\[x^2+y^2+2gx+2fy+c=0\]	\[(x+g)^2+(y+f)^2=2(g^2+f^2-c)\]