# Find the relation so that the two circles $x^2+y^2+2gx+2fy+c=0$ and $x^2+y^2+2g_1x+2f_1+c_1=0$cut each other orthogonally.
$\begin{array}{1 1}(a)\;c+c_1=2gg_1-2ff_1\\(b)\;c+c_1=2gg_1+2ff_1\\(c)\;c+c_1=gg_1-ff_1\\(d)\;c-c_1=2gg_1+2ff_1\end{array}$