Prove that the general equation of circles cutting the circles `x^2 + y^2 + 2g_r x + 2f_r y+c_r = 0, r= 1, 2` orthogonally is : `|(x^2+y^2,-x,-y),(c_1,g_1,f_1),(c_2,g_2,f_2)|+k|(-x, -y, 1), (g_1, f_1, 1), (g_2, f_2, 1)|`=0