Find the polar of 

(a) (1,2) with respect to $x^2+y^2=7$

(b) (3,-1) with respect to $2x^2+2y^2=11$

(c) (1,-2) with respect to $x^2+y^2-10x+10y+25=0$

(a) Polar of (1,2) w.r.t $x^2+y^2=7$
                                $\begin{array}{l}{\mathrm{S}}_1=0\\ {\mathrm{xx}}_1+{\mathrm{yy}}_1=7\\ \mathrm{x}\left(1\right)+\mathrm{y}\left(2\right)=7\end{array}$
(b)Polar of (3,-1) w.r.t $2x^2+2y^2=11$
                                 $2x\left(3\right)+2y(-1)=11$
                                $6x-2y=11$
(c)Polar of (1,-2) w.r.t $x^2+y^2-10x+10y+25=0$
                                  $\begin{array}{l}{S}_1=0\\ x\left(1\right)+y(-2)-5(x+1)+5(y-2)+25=0\\ -4x+3y+10=0\\ 4x-3y-10=0\end{array}$