What is the condition for two circles x2+y2+2g1x+2f1y+c1=0x^2 + y^2 + 2g_1x + 2f_1y + c_1 = 0x2+y2+2g1x+2f1y+c1=0 and x2+y2+2g2x+2f2y+c2=0x^2 + y^2 + 2g_2x + 2f_2y + c_2 = 0x2+y2+2g2x+2f2y+c2=0 to be orthogonal?
2g1g2+2f1f2=c1+c22g_1g_2 + 2f_1f_2 = c_1 + c_22g1g2+2f1f2=c1+c2
g1g2+f1f2=c1+c2g_1g_2 + f_1f_2 = c_1 + c_2g1g2+f1f2=c1+c2
g1g2+f1f2=2(c1+c2)g_1g_2 + f_1f_2 = 2(c_1 + c_2)g1g2+f1f2=2(c1+c2)
g1g2+f1f2=c1c2g_1g_2 + f_1f_2 = \sqrt{c_1c_2}g1g2+f1f2=c1c2