从几何直观可知,双曲线与其渐近线分别将平面分为两部分,其中含有焦点的区域分别叫内域与内角域,不含焦点的区域分别叫外域与外角域,显而易见,内域是内角域的其子集,外角域是外域的其子集。 From the geometrical intuition we can see that the hyperbola and its asymptote respectively divide the plane into two parts. The areas containing the focus are called the inner area and the inner angle area respectively. The areas without the focus are called the outer area and the outer angle area respectively. Obviously, the inner area is the inside angle. The subset of the domain, the outer angular domain is a subset of the outer domain.