Let the right focus be F(C, 0), then the radius of the circle is 2C and the center of the circle is F(C, 0). The equation of a circle is (X-c)*2+Y*2=4C*2. It passes through points (b, 0), (0, b). Substitute these two points! ! That's the step, and then according to e=C/a, it comes out! I want to return it. It's inconvenient to calculate ~ ~ ~ This is the only way to provide it! !