圓心 \(\displaystyle{C\left( h,k \right) }\): 
半徑 \(\displaystyle{ r = }\) 
點 \(\displaystyle{ Q\left( {{x}_{0}},{{y}_{0}} \right) }\): 
線段 \(\displaystyle{ CQ }\): 
\(\displaystyle{{{x}_{0}}^{2}+{{y}_{0}}^{2}+D{{x}_{0}}+E{{y}_{0}}+F}\)  0
結論: